Programming Ruby
Marek Hulán, Marek Jelen, Ivan Nečas
Version 0.1, October 14, 2016
Table of Contents
Ruby basics...................................... 1
1. Instalation.............................................................................2
1.1. Linux.................................................. 2
1.2. Windows...........................................................................2
1.3. macOS..................................................... 2
2. Running Ruby..........................................................................3
2.1. Interactive Ruby....................................................................3
3. About Ruby .............................................. 4
3.1. Interpreted ........................................................................4
3.2. Universal..........................................................................4
3.3. Fully Object oriented................................................................4
3.4. Everything is an expression..........................................................4
3.5. Atomic memory management........................................................4
3.6. MRI................................................................................4
3.7. Strongly typed .....................................................................4
3.8. Dynamically typed..................................................................4
3.9. What is written in Ruby?....................................... 5
4. Conventions............................................................................6
5. Basic syntax............................................................................7
5.1. Operator priority...................................................................7
5.2. Special characters in method names..................................................7
5.3. Comments.........................................................................7
6. Data types.............................................................................9
6.1. Strings............................................ 9
6.2. Numbers...........................................................................9
6.3. Empty value................................................ -9
6.4. Booleans....................................................... 9
6.5. Arrays............................................... 10
6.6. Hashes ..................................................... 10
6.7. Symbols..........................................................................10
7. Objects and methods.................................................................. 11
8. Variables............................................................................ I2
9. Conditions........................................................................... 13
10. Logical operators.....................................................................15
11. Regular expressions....................................... 16
12. Loops.................................................. 17
13. Methods............................................................ .......18
14. Reusing code from other files ....................................................... 19
15. Blocks..................................................... 20
16. Objects............................................................................. 22
17. Inheritance........................................ 23
18. Class methods and attributes................................. ........24
19. Modules................................................ 25
20. Method access........................................................................26
21. Duck typing......................................................................... 27
22. Exceptions........................................... 28
Advanced Ruby............................................................................29
23. Return values...................................... 30
24. Context..............................................................................31
25. Class......................................................... 32
25.1. Open classes........................................... 32
25.2. What is a class?...................................................................32
25.3. Inheritance................................................... 33
25.4. Mixins......................................................................... 33
25.5. Class introspections................................. 34
26. Methods ............................................................ 35
26.1. Extracting methods................................. 35
26.2. Checking method existence........................................................35
26.3. Dynamic method calling..........................................................36
26.4. Defining methods programmatically ..............................................37
26.5. Missing methods.................................................................38
27. Objects........................................................ 39
27.1. Creating new object .......................................................... 39
27.2. Defining methods ............................................. 39
27.3. Eigenclass .................................. 40
27.4. Method lookups......................................... 42
Testing ..................................................................................45
28. Testing frameworks................................................................. 46
29. Minitest................................................ 47
29.1. Testunit syntax................................................ 47
29.2. Assertions...................................................................... 47
29.3. Spec syntax......................................................................48
29.4. Output of test run................................................................49
29.5. Running multiple test files....................................................... 49
29.6. Test coverage ............................................ 50
29.7. Stubbing .......................................................................50
29.8. Mocking .......................................................................51
29.9. Stubbing network calls.......................................... 52
29.10. Testing web applications .............................................. 53
29.11. Cucumber......................................................................54
Standard library & libraries ................................................................56
30. Files.............................................................................. 57
Ruby on Rails..............................................................................58
31. Introduction.........................................................................59
Ruby basics
Get started with Ruby
l
Chapter 1. Instalation
1.1. Linux
^        Do not use prepackaged Ruby on Linux distributions. On Linux use rbenv package manager with the ruby-bui Id extension to install Ruby.
1.2. Windows
For windows there is an installer Ruby Installer simplifies the installation to the "windows standard approach".
1.3. macOS
The simplest way to install Ruby on macOS is to use homebrew package manager
$ brew install ruby
in case there is a need to have multiple installations rbenv is a good tool to use. Another popular tool is called rvm but nowadays they do too much magic and we recommend using rbenv instead.
2
Chapter 2. Running Ruby
f\ Usually you put ruby and relates command on PATH so you do not need to always • specify the whole path to the executable. With tools like rbenv this is done for you.
$ ruby -v
runs Ruby and prints it's version. Simplest way to verify that your instalation works as expected.
/-\
$ ruby script.rb
interprets the script.rb. However instead of running the script explicitly, you can add the shebang line to your script
#!/usr/bin/env ruby
and make it executable (chmox +x script, rb) and run it simply as ./script.rb.
2.1. Interactive Ruby
Ruby comes with an interactive interpreter called i rb it allows you to enter commands and see results instantly.
$ i rb
3
Chapter 3. About Ruby
Ruby a programming language with following aspects
3.1. Interpreted
The Ruby code is interpreted when the script is load, there is no compile phase.
3.2. Universal
Ruby can be used for writing scripts, one-liners, web applications and even for mobile and desktop applications.
3.3. Fully Object oriented
In Ruby everything is an object and you send messages to those objects.
3.4. Everything is an expression
Everything command in Ruby has a return value.
3.5. Atomic memory management
3.6. MRI
MRI is the Ruby reference implementation, with several other implementations like JRuby, Rubinius, IronRuby or MagLev. As well, there is ISO standard implemented in mruby.
3.7. Strongly typed
There are some implicit conversions (e.g. every object has to_s method to provide string representation) but in most cases in case you try to operate on different types Ruby will complain, unless such operation is explicitly provided.
5 + "a" # => TypeError: String can't be coerced into Fixnum
3.8. Dynamically typed
The type of a variable is defined by the value assigned to that variable. There is no explicit type information in the code.
<->
a = "string"
4
3.9. What is written in Ruby?
• programming languages: Ruby (Rubinius), compilers (LessJS)
• web applications: Github, Gitlab, Redmine, BaseCamp
• devops tools: Puppet/Chef/Vagrant
• cloud platforms: OpenShift (v2)
• cloud management: Foreman, ManagelQ
• VIM/Emacs scripts
• static pages generators - Jekyll
• programming tools
Chapter 4. Conventions
• class names are CamelCase
• file names reflect class names in snake_case format
• method names are snake_case
• constants are UPPER_CASE
• indent by 2 spaces
• methods returning boolean values end with ?
• methods mutating state end with !
6
Chapter 5. Basic syntax
Basic and most explicit syntax looks like
puts("hello world!");
However the parenthesis are optional in case the only one interpretation of the expression
puts "hello world!";
and semicolons are optional as well
puts "hello world!"
String use either quotation marks " or apostrophes '. Apostrophes does not provide string substitution as quotations marks do.
a =	'Hello'	#	=>	-"Hello"
b =	"#{a} world"	#	=>	"Hello world"
b =	'#{a} world'	#	=>	"\#{a} world"
5.1. Operator priority
5.2. Special characters in method names
Ruby allows usage of special characted in method names. The standard is to use
• the question mark ? for methods that return boolean value
• the exclamation mark ! for methods that mutate the object
1 .even?	#	=>	false
"ruby".upcase.reverse	#	=>	'YBUR'
"ruby".size.even?	#	=>	true
5.3. Comments
In the code above the single line comment is used. It starts with hash # and follows to the end of the line. In case of commenting multiple lines, it is customary to comment every line with single line comment.
7
I-\
# you should
# do this
# to comment
# multiple lines
8
Chapter 6. Data types
As mentioned above in Ruby everything is an object, including arrays or numbers. However there are special syntax shorthands to create instances of special classes.
6.1. Strings
As mentioned above String are create by quoting the charachters
a = "string" b = 'string'
6.2. Numbers
Ruby has two basic number classes Fi xnum and Float.
a = 1 tt
a.class # => Fixnum
b = 1.1 # =
b class # => Float
6.3. Empty value
Special value that represents "nothing" is ni 1.
t-<
a = nil # => nil
In a boolean expression, nil is considered false, i.e. it's only of two possible values that are not considered true.
6.4. Booleans
As usual there is either true or false.
					
a	= true	#	=>	true	
b	= false	#	=>	false	
a	&& b	#	=>	false	
a	II b	#	=>	true	
9
6.5. Arrays
Arrays is an ordered sequence of values. There are no restrictions on what types can be in a single array.
["a", 1, true] # => ["a", 1, true]
6.6. Hashes
Hash is a structure that maps key to a value.
/-\
{"a" => true, "b": false} # => {"a"->true, :b->false}
There are two approaches how to write the mapping, either rocket style
key => value
or j son style
key: value
You can use both syntaxes, however with the j son style the value is converted to symbol, so in case you need to use Stri ng or some other type, or get the name of the key from a variable, you need to use the rocket style. Several well-known coding guidelines recommend (and enforce) using rockets everywhere.
6.7. Symbols
Symbol is a keyword. It always maps to the same object instance
a =   a   # => a	
L              11__11     U         ^      " ^ " b =   a   # => a	
a.object_id # =>	70224766839340
b.object_id # =>	70224750415480
a = :a # => :a	
b = :a # => :a	
a.object_id # =>	722268
b.object_id # =>	722268
10
Chapter 7. Objects and methods
Methods are called by using the .. Operators are actually methods.
3+3 # => 6 3.+(3) # => 6
[1,2][0] #=> 1 [1,2].[](0) # => 1
11
Chapter 8. Variables
Ruby has global variables prefixed by $.
Classes and object can use class variables, though there are not used very much. Prefer @i nstance_vari ables in class-level methods, as they have more predicatable behavior.
@@class_variables = 1 Objects have instance variables.
Local variables have no prefix.
local variable = 1
And finally constants are all upper case.
CONSTANT = 1
12
Chapter 9. Conditions
Everything is considered true except false and nil.
a = nil b = ""
if a
"we do not get in here" elsif b
"we got here" else
"we did not get here" end
Ruby has negative variant to if called unless. Essentially unless bool_expr is equivalent to if ! (bool_expr). It is used the same way as normal i f.
a = nil b = ""
unless a
"we do get in here" elsif b
"we did not get here" else
"we did not get here" end
Ruby has inline method of using conditionals called modifier statements.
puts "Hello" if true puts "Hello" unless false
Ternary operator is available as well.
experssion ? 'was evaluated true' : 'was evaluated false'
Another way to do conditions is to use case statement.
13
I-\
case input when 'q', 'e'
quit when 'f
format else
help
end
Case statement can as well check on variable class.
case var when String
"it's string" when Class
"it's class" when Number
"it's number"
end
Another way to use case statement is to use it as i f and elsi f.
case when a == "a"
"a equals a" when b == "b"
"b equals b"
end
14
Chapter 10. Logical operators
There are basic logical expressions
• and&&
• or 11
• not !
as well && can be replaced with and, 11 can be replaced with or and ! can be replaced with not. There are basic comparison operators
• equal ==
• not equal ! =
• lesser then <
• greater then >
• lesser then or equal
• greater then or equal >=
• regular expression match =~
15
Chapter 11. Regular expressions
Regular expressions are enclosed with /. The simplest way is to use the regexp operator.
string = 'localhost:2000' string =-/.*:.+/ #0 string =~ /(.)*:(.)+/ # sets $1 a $2
as well there is a match method on string.
data = string.match(/A(.):(\d+)$/) data[1] # => localhost data[2] # => 2000
16
Chapter 12. Loops
while repeats as long as the condition is true.
while a < b
a += 1 end
To go through the body of the loop at least once
begin
a += 1 end while a < b
There is as well inline way to write the loop
a += 1 while a < b
And finally the negative counterpart unti 1
until a > b
a += 1 end
17
Chapter 13. Methods
Methods in Ruby always return some value. If it is not explicitly returned using the return keyword, the return value is the value of the last expression in the method. Return as usual returns from method and ends the execution of the method.
,--•
# Simple method with two arguments def mth(a, b)
end
# Method with default value for 2nd argument def mth(a, b=1)
end
# Method accepting any number of arguments, available as Array args def mth(*args)
end
# Method requiring at least two arguments def mth(a, b, *args)
end
18
Chapter 14. Reusing code from other files
The require method loads code from another file. Ruby keeps track of required files and skips loading files that would be loaded 2nd time. Files are looked up using Ruby's load path, which is represented using an array in $L0AD_PATH and $:. The load method does not keep track of loaded files.
In case the required file ends with [rb, so, o, dll, bundle, jar] extension, the extension may be omitted. There two commands are equivalent
require "somefile" require "somefile.rb"
To keep track of required files, Ruby keep list of all files that were required in the $" variable.
19
Chapter 15. Blocks
Blocks have many uses-cases. One of the use cases is the replacement for for cycles another use case is anonnymous functions. Block are not executed when defined, but have to be called through the call method (though the calling of call method is most of the times hidden from the develop as in the examples below).
Arrays have method called each that accepts block and calls the block for every single element in the array.
arr = [1,2,3,4] arr.each do |el|
puts el end
will print all four values to the standard output. Blocks can be written in one more way
arr = [1,2,3,4]
arr.each { |el| puts el }
this variant is usually used for single-line blocks.
Block see their own scope plus can access scope in which were defined.
sum = 0
arr = [1,2,3,4]
arr.each { |el| sum += el }
Any method can accept a block and call it def mth
return nil unless block_given? yield end
This method will return nil if no block was given or will call the block without any argument and the return value of the block will be return from the method.
Method may also accept blocks as a named argument which is prefixed by &.
def mth(num, &block)
block.call(num) end
20
this method will call block saved in the variable block and will pass one argument which is the first argument passed to the method itself.
21
Chapter 16. Objects
In Ruby everything is an object. Object is an instance of some class. Even every class is an instance of class that inherits from Class. Object can have methods
class Hello
def say "Hello, world!"
end end
puts Hello.new.say
and instance variables
class Hello def initialize(msg=nil)
@msg = msg end
def say @msg end end
puts Hello.new("Hello, world!").say
To make your instance variables accessible from outside, you define them as attributes. Attributes can be either read-only, write-only or both.
class Hello		
attr_reader :	one	# allows reading by using the .one method
attr_writer :	two	# allows writing by using the .two = "xy" method
attr_accessor	:three	# allows both, reading and writing
end		
22
Chapter 17. Inheritance
Ruby allows object inheritance. All methods including constructor are inherited. Methods can be overridden by children, super is then used to call the original method.
class A
def a "hello"
end end
puts A.new.a # => hello
class B < A end
puts B.new.a # => hello
class C < A
def a super + " world"
end end
puts C.new.a # => hello world
23
Chapter 18. Class methods and attributes
As known from other language, except in Ruby class variables are not used because of some pitfalls in their inheritance.
class A
def self.a "hello"
end end
puts A.a # => hello
24
Chapter 19. Modules
Modules are a way to organize your classes in a similar fashion to namespaces. Classes can be included into modules or into other classes.
class A	-
class B	
end	
end	
module Some	
class Thing	
end	
end	
Module are however used as well as mixins. When module is included into class all methods defined for that module are available in the class as instance methods.
module Helper
def something end end
class A
include Helper end
A.new.something
and when used with extend the mehtods are included as class methods
module Helper
def something end end
class A
extend Helper end
A something
Ruby has only single inheritance, mixins allow to get around this and provide a way to get some kind of multiple inheritance.
25
Chapter 20. Method access
By default methods are public, explicitly methods can be made protected or private.
class A def publicjnethod end
protected
def protected_method end
private
def private_method end end
26
Chapter 21. Duck typing
Ruby encourages to react based on behaviour rather then on identity.
class Hunter
def shoot(animal) bang! if animal.class == Duck
end end
in this case the code checks if it's a duck and shoots it, however
class Hunter
def shoot(animal) animal.respond_to?(:quack) && bang!
end end
in this case we care if the animal quacks and the it's shot.
Chapter 22. Exceptions
Exceptions represnt a special state in the execution in a program. When an exception is raised, it will bubling thorugh the stack until is caught.
Exceptions are raised using the rai se keyword
t-<
raise "This is not expected"
On the other hand when an exception needs to be caught, code block is extended with rescue statement that is called when an exception is caught and optionally ensure that is called after both exceptional and non-exceptional state. Unless an exception class is specified explicitly after the rescue keyword, the StandardError class and it's ancestors are rescued.
begin
raise "This is not expected" rescue => e
puts e.message ensure
puts "always" end
Don't inherit directly from Exception class but use StandardError instead. The direct descendants of Exception are usually exceptions one doesn't want to rescue from, such as SystemExit or NoMemoryError.
28
Advanced Ruby
Meta-programming, DSLs, etc.
29
Chapter 23. Return values
In Ruby everything is an expression - it executes and returns some value, the result of it's execution. Let's take a look at a simple example
5 + 2	#	=>	-7
"hello"	#	=>	"hello"
"a" if true	#	=>	"a"
"a" if false	#	=>	nil
class A; end	#	=>	??? *
What is the result of the last expression? It could be obvious - "we defined class A". But not really. The fact we have defined a class is only an effect of the expression but not the result, result is a value returned from the expression itself.
/-\
class A; end # => nil
The result is simply nil. It's similar to the expression "a" if false above. The condition is evaluated as false and there is no else so there is nothing to return, so the result is ni 1. In this case a class was defined, but there was nothing to be return, as the body of the class was empty, so the result is nil. Let's modify the example to return a value
class A;	1; end	#	=> 1
class A;	1; "hello"; end	#	=> "hello"
class A;	self; end	#	=> A
Before it was said that the return value of a method is the result of it's last expression. And it's obvious that in this example it's very similar, and it can be generalized for all structures, even though sometimes it may not be obvious on the first sight.
the return value is the the result of the last expression
30
Chapter 24. Context
In Ruby everything is executed in some context. This context is know as current object and is always represented by self.
self.class	#	- ^ => Object
class B self end # => Class		
class A def call self end end		
A.new.call	#	=> #<A:some number>
31
Chapter 25. Class
25.1. Open classes
Unlike most languages, Ruby classes are open for modifications. Developers can modify behavior of classes defined by frameworks or Ruby itself. This technique is called Monkey patchi ng.
class Clazz
def call "A"
end end
class Clazz
def call "B"
end end
Clazz.new.call # => "B'
25.2. What is a class?
Let's start with a definition
classes are instances of class Class
and as mentioned many times before, everything in Ruby is an object... even a class.
32
t- class A			-
def self.	call		
"A"			
end			
end			
B = Class.new			
def B.call			
"called"			
end			
A.call	#	=>	"called"
B.call	#	=>	"called"
A object_id	#	=>	[some number]
B.object_id	#	=>	[some number]
A.class	#	=>	Class
B class	#	=>	Class
Class A was defined using the class keyword and then a class method was defined. Class B was created by creating new instance of the Class class and the object was assigned to constant B. As both of those classes are objects, it's possible to check it's class and the ID of the object.
25.3. Inheritance
In Ruby classes can inherit from each other, though Ruby has only single-class inheritance - it's not possible to inherit from multiple classes, only from one.
class A	
def call	
"called"	
end	
end	
class B < A	
end	
C = Class.new(B)	
B.new.call # =	'called"
C.new.call # =	'called"
25.4. Mixins
When some class needs to inherit from multiple classes, it's not possible, but Ruby provides a
33
workaround through mixins. It is possible to include many Modules into a class the methods defined in those modules will become part of the lookup path as if they were defined in the class.
module Methods
def call "called"
end end
class A
include Methods end
A.new.call # => "called"
25.5. Class introspections
Ruby allows many introspections on classes and many other objects.
There is method name defined on a class that returns the name of the current class.
Array.name # => "Array" [].class.name # => "Array"
It's possible to list methods of an object
/-
class A
def call
end end
A.new.methods # => array of methods
34
Chapter 26. Methods
As everything else in Ruby even methods are instances of class Method.
26.1. Extracting methods
Sometimes it is useful to pass around only a method instead of the whole object. Ruby allows extraction of a method for later usege.
class A
def call(argl) self
end end
meth = A.new.method(:call) # => #<Method: A#call>
In the example method call from class A was "extracted". The method is still bound to the instance of class A and the method will be evaluated in the context of the object (self will be the instance). The method can be executed by calling the call method with appropriate arguments.
meth.call("some string") # => #<A:some_number>
26.2. Checking method existence
Because Ruby is a very dynamic language, it's not possible to know in advance what kind of arguments will be received. In most cases the developer should not care what class the argument is, but whether the argument responds to a method.
Do not care what the object is, only care whether it behaves as expected.
This technique is called Duck typing.
class A	
def call	
end	
end	
a = A.new	
a respond_to?(:call) #	=> true
a respond_to?(:wtf) #	=> false
35
26.3. Dynamic method calling
Let's define a class with a method, create an instance and call the method.
class A
def call
end end
A.new.call
The method is called, but the develeoper had to know the name of the method beforehand ... in the time the code is written. What if the method name is not known and there has to be some method called. Do not be surprised, this is very common use-case in Ruby
class A
def call(argl)
end end
a = A.new
a.call("some string") a.send(:call, "some string")
Well, not so identical. When you use the send method on an object, you effectively bypass the access modifiers.
Ruby has three access levels public is default, protected and private.
36
class A	>
def publicjnethod	
end	
protected	
def protected_method	
end	
private	
def private_method	
end	
end	
a = A.new	
a.publicjnethod	nil
a.protected_method   # =>	NoMethodError: protected method 'protectedjnethod' called ...
a.private_method	NoMethodError: private method vprivatejnethod' called ...
a.send(:publicjnethod)	# => nil
a send(:protectedjnethod)	# => nil
a.send(:private jnethod)	# => nil
26.4. Defining methods programmatically
The way to define methods using the def keyword shown before is not the only one. It's also possible to define method in a more dynamic way. It makes sense. We can inspect methods of an object, we can extract methods of an object and also call methods of an object in a dynamic way. To dynamically define a method use the def i ne jnethod method of a class, however
Class.definejnethod is private
To get around this obstacle, it's possible to use the send method and bypass the access modifier.
37
I-\
class A end
a = A.new
logic = Proc.new do
"data" end
A.send(:define_method, :some_method_name, logic) a.some_method_name # => "data"
26.5. Missing methods
Every object can define special methodjnissing method that is called whenever there is a call to undefined method on that object.
class A
def method_missing(name, *args, &block)
puts "method #{name} called with args #{args.inspect}" end end
A.new.somethingC'a") # => method something called with args ["a"]
38
Chapter 27. Objects
Objects complement classes in a way that
objects define state and classes define behavior
Behavior id defined as a class, then an object is created for that class to hold the state. Every object has to be of some class.
27.1. Creating new object
To create an object of a class there is the new method on respective class.
class Dog end
dog = Dog.new
27.2. Defining methods
In the example above many methods were defined in simple or more fancy styles. But let's get back to the core and try to define a method
class A
def call
end end
here we use def keyword to define method call. Where will def define the method? The answer is simple and complex
def defines methods into the nearest class
So in the previous example the nearest class is A. That is obvious from next example where the current context is returned and inspected
var = class A; self; end
var.class   # => Class var.name    # => "A"
OK, so the the current context is a Class and thus is't obvious that the nearest class is this class. Now
39
let's try to define a class method
class A
def self.call "string"
end end
Where will Ruby define the method now?? It is a bit more complicated. To understand this, we have to explain something else first.
27.3. Eigenclass
To understand how Ruby works, we have to understand what eigenclasses are. Let's start with simple definition
every object in Ruby has it's own eigenclass => an instance of Class
eigen means "it's own" in German
Why is this important? Because, however the eigenclasses are basically invisible to developers, they take an important part in method lookups.
When Ruby is trying to look up a method, it follows a basic chain (will be described a bit later). Important is, that before the class the object is linked to, there is the one more class - object's eigenclass. Every single object in Ruby has it's own eigenclass and because Classes are object as well, eigenclasses has their own eigenclasses as well.
The closest class to an object is not it's class but it's eigenclass.
Back to the example we were talking about
class A def self.call
"string" end end
to see it more clearly we can rewrite this example identically as
40
f-
class A end
def A.call "string" end
these two expressions are identical. To understand why it is important to understand this
class A end
scope = class A
self end
A == scope # => true
but back to the original question ... where is the method going to be defined? In the context of the instance of the class A. The important part is the instance of. What is the closest class to an instance (object)? As stated above it's its eigenclass. Now you might have guessed that from implementation point of view
there are no class methods in Ruby
What would be called a class method is only an instance method defined on the eigenclass associated with object representing the class.
So eigenclass	is some stealth object that we can not see? Not really. Ruby has ways to access
eigenclasses	
eigenclass	-= class « some_object
self	
end	
eigenclass	= some_object.singleton_class
now that we can access eigenclasses, let's see how we could define "class methods" (instance methods in the eigenclass).
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class A
def self.call "called"
end end
class B class « self def call
"called" end end end
D = Class.new class « D
def call "called"
end end
all those examples are identical.
27.4. Method lookups
Now that you know where and how are methods defined, lets see how methods are looked up. Let's see how the class hierarchy looks for class
SomeClass -> Class -> Module -> Object -> BasicObject
and for objects
/-\
object -> SomeClass -> Object -> BasicObject
though in real it is a bit more complex as seen in this picture
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Eigenclasses are not visible as classes of objects.
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I-\
o1 = Object.new
def o1.meth
"string" end
01. meth   # => "string"
01 .class # => Object
02 = Object.new
02. meth   # => undefined method 'meth' o2.class # => Object
This example shows that having two instances of same objects. Both can behave differently. Because in the case of ol the method is stored in the eigenclass, that is not accessible by o2.
Eigenclasses are used when a specific behavior of an object is expected.
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Testing
Writing automated tests for the code is essential. Ruby community emphasizes it and most of projects are well covered. A TDD is also popular among rubyist.
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Chapter 28. Testing frameworks
Today de facto standard is to use Minitest testing framework. You can see RSpec being still used too but Minitest already offers the capabilities and more. Both can be easily used for TDD. For BDD there's popular ecosystem called Cucumber which started as Ruby gem but quickly evolved into polyglot tool.
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Chapter 29. Minitest
A syntax you can see in tests can be in two forms. Either something we call testunit (aka junit) and spec that was taken from Rspec. The internal implementaion is the same for both and it's mostly matter of taste. However tests are regular ruby scripts that test other scripts. Test are usually to be found at test/ directory, file name should reflect test class defined inside, e.g. morse_coder_test.rb.
Example output of
29.1. Testunit syntax
require 'minitest/autorun' require 'morse_coder.rb'
class MorseCoderTest < Minitest::Test def setup
@coder = MorseCoder.new(...) end
def test_encode_for_single_letters assert_equal @coder.encode "a"
assert_equal @coder.encode "b"
end end
Test class should inherit from Minitest: :Test so test helpers (assertions) are available. Testing methods must start with "test_". Other methods are regular methods that can be used from testing methods, e.g. to build some fixtures.
There are few method names with special meaning. In the example you can see method with name setup. This method gets automatically executed before every testing method. Similarly there's teardown method that get's executed after each testing method. It's usually used for cleaning up mess the testing method created.
29.2. Assertions
One testing method can contain more than one assertion. First assertion failure stops the method run and mark the test as failure (F). If method raises an exception the result of test is marked as error (E). If all assertions defined in method passes, test succeeds (.). If you plan to implement the test later you can skip the test by calling ski pC'Sorry, I'm lazy").
The simplest assertion is to test boolean value like this
assert gsomething
This will succeed if ©something is considered true, fail otherwise. The negative form is refute, e.g.
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following would pass.
refute false
You could obvisouly add tests like assert gsomething == ' that I expect' but it would generate very generic messages on failures. You can specify custome message by passing extra argument like this
assert gsomething == 'that I expect', '@something does not match expected string'
but it's always better to use assert helper that matches the use-case best. Following example demonstrates how to check equality of two values, the failure message would automatically include information about what's it ©something and what was expected it to be.
assert_equal gsomething, 'that I expect'
Useful assert helpers are listed in example below. All of them can be found in Minitest documentation.
'- assert arg	# arg is true
refute arg	# arg is false
assert_equal	expected, actual
assert_includes	collection, object
assert_kind_of	class, object
assert_nil	object
assert_match	expected, actual
assert_raises -	exception_class &block
29.3. Spec syntax
Subjectively better structured, less repeating, more readable and TDD supporting syntax can be used. See the following example.
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I-\
require 'minitest/autorun' require 'morse_coder.rb'
describe MorseCoder do let(:coder) { MorseCoder.new(...) }
describe 'single letters encoding' do let(:a) { coder.a } let(:b) { coder.b }
specify { a.must_equal '.-' } specify { b.must_equal '-...' } end end
Describe block wraps logical block. Each such block can have it's own before (aka setup). With let we define method that can be called later within any nested block. Let is lazy, speci fy accepts a lock that uses assertion helpers in form of must_$assert or wont_$assert. There are many other extensions to this language so it reads more naturally.
Note that since the implementation is the same, you can combine both at the same time.
29.4. Output of test run
Run options: --seed 25127 # Running tests: . .S.....F........
Finished tests in 101.524752s, 6.4319 tests/s, 9.0618 assertions/s 63 tests, 92 assertions, 1 failures, 0 errors, S skips
1) Failure:
TestConnector#test_connection [./connector.rb:5]: Expected: nil Actual: "that I expect"
The seed is random number representing the order of test. Note that your tests should be order indpenendant.
29.5. Running multiple test files
It's common to have more than just one test file in project. To run all tests at once we can use Rake. Usually tests are put in test directory in the project tree structure. In such setup we can easily define test task in Rakefile. Rake provides built-in class for this, we just need to configure it. Just put following into your Rakefile.
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I-
require 'rake/testtask'
Rake::TestTask.new do |t| t.libs « 'test'
t test_fil.es = Dir.glob('test/**/*_test.rb') t.verbose true end
we can run rake test which will load a run all ruby scripts with _test suffix in the test directory including all of its subdirectories. If you prefer test to be the default rake task, add following to the Rakefile
task :default => [ :test ]
now you can run all tests just by running rake.
Another common practise is to have one file that is loaded at start, usually named test_helper.rb. This file contains everything that is needed for all tests, like requiring additional testing libraries. You can also put requi re mi ni test/autorun there. Just note that you need to requi re ' test_helper' as first line of every test file.
29.6. Test coverage
To get a good overview of what needs test coverage it's useful to setup code coverage check. A simplecov gem can generate html report. Just put following on top of you test_helper.rb
require 'simplecov' SimpleCov.start
you can also define a minimum coverage in percents
SimpleCov.minimum_coverage 95
Now when you run your test suite, new directory called coverage will be created. See coverage/i ndex. html for details how well your code is covered with tests.
29.7. Stubbing
Sometimes we don't want to call all method chain when we test just single method behavior. This applies especially in unit testing where we test just small piece of code. Since Ruby is dynamic language, it's easy to cut off some methods. This is called stubbing (leaving stubs).
Let's look at following example
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I-\
class TemperatureMeter
def measure(output)
temp = rand(21) + 20
output.puts temp
temp end end
The test covering this should call method measure and verify it returns reasonable temperature. We don't want our test to print anything to STDOUT. We can stub out puts method easily like this
	
def test_measure	
meter = TemperatureMeter.new	
STDOUT.stub(:puts, nil) do	
result = meter.measure(STDOUT)	
assert_kind_of Fixnum, result	
assert_includes 20..40, result	
end	
end	-
With this stubbing, puts method is replaced by new empty method that returns the second argument, in this case nil. The stub is applied only within the stub block.
29.8. Mocking
Mocking is related to stubbing. Imagine we wanted to check that measure method really called puts on output object. The method is written in a way that it accepts custom output object, which makes testing easy. We can simply pass any object that implements method puts, e.g. file handler, socket or our own testing object. Or we can use mocks. Mock is a blank object on which we can define expectations.
For example we can create a mock instance and specify that its method puts should be called exactly once during the test.
t-<
def test_measure_print_the_value
meter = TemperatureMeter.new
mock = Minitest::Mock.new
mock.expect(:puts, nil, [20..40])
result = meter.measure(mock)
mock.verify end
First expect argument is the name of method to be called, second is the return value and third is the array containing arguments which the puts should be called.
You could also stub the rand method to return let's say 0 and then setup expectation that mock's puts
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method will receive 20 as a parameter to print. But the range also works so the mock accepts any value between 20 and 40.
You have to call verify on mock so it runs assertions on how many times the expected method was called. To expect another call of puts, just define new expectation with .expect.
29.9. Stubbing network calls
If your app communicates with external services over HTTP you most likely need to fake the communication in your test suite. Reasons include performance, spamming of remote services, avoiding credentials leaks, error state testing. Constructing the whole net/http response object can be complicated. Luckily there are tools that can help you greatly.
First is webmock gem. It provides helpers to stub low-level methods easily. To use it, install the gem and just add following to your tests.
require 'webmock/minitest' stub_request(:get, 'www.example.com')
Net::HTTP.get('www.example.com', '/') # this will succeed
You can also specify more conditions to match the request as well as return value
t-<
stub_request(:post, 'www.example.com').with(:body => 'ping').to_return(:body => 'pong')
Custome headers can be added too. Webmock works with higl level libraries such as popular Restclient gem.
Another useful tool is vcr. The name was chosen because of analogy with videocassette recorder. It can record a real network communication and replay it later. This can be nicely used in tests. You only record the communication once during writing tests and replay it while running tests in future or on CI server. You can have multiple communications recorded and just swap cassetes for each test. Example follows
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I-
require 'vcr'
VCR.configure do |config| config.cassette_library_dir = "fixtures/vcr_cassettes"    # storage for cassetes config.hook_into :webmock # webmock integration
end
class VCRTest < Minitest::Test def test_example_dot_com VCR.use_cassette("success_info") do
response = Net::HTTP.get_response(URI('http://www.example.com/')) assert_match /Example Domain/, response.body end end end
29.10. Testing web applications
If you work on web app you can also easily test the interaction like users will interact through web browser. This is useful when you write integration tests. A de facto standard is capybara gem that provides drivers for various browser backends. The simplest to setup driver is RackTest, so you can start with it as long as your app uses rack.
If you need advanced stuff like testing pages with asynchronous requests through AJAX you can use Selenium driver which runs firefox in headless mode. If you want to run such tests on CI server without XI1 server, there's Poltergeist driver using PhantomJS.
An example of simple test, supposing my_app.rb contains rack based app (e.g. using Sinatra).
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require 'minitest/autorun' require 'capybara/dsl' require './my_app.rb'
Capybara.app = MyApp Capybara.default_driver = :rack_test
class MyAppTest < Minitest::Test include Capybara::DSL
def test_index visit '/'
click_link 'login' fill_in('Login', with: 'Marek') fill_in('Password', with: 'secret') click_button('Submit')
assert page.has_selector(1div p.success') assert page.has_content?('Welcome Marek') end
def teardown
Capybara.reset_sessions!
Capybara.use_default_driver end end
29.11. Cucumber
We can use Cucumber framework for BDD aproach. It allows us to write the behavior specification in natural language first and then convert it to test step by step. Imagine you'd describe a feature like this
Feature: logout of logged in user
Scenario: User can log out from app Given I'm logged in as user ares
And I'm on host list page When I click logout link Then I should see logout notification
It's a valid cucumber test (aka feature) which only needs implementing those steps, usign capybara for example.
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Given(/AI'm logged in as user (.*)$/) do |user| visit '/'
fill_in "login", with: user fill_in "password", with: 'testpassword' click_button 'login' end
Given(/AI'm on (.*) (.*) page$/) do |resource, action
visit "/#{resource}/#{action}" end
When(/AI click (.*) link$/) do | identifier|
click_link identifier end
Then(/AI should see logout notifications/) do
assert page.has_content 'div p.logout_notification' end
One advantage that it brigns is, that your tests are live documentation too.
Standard library & libraries
Get the know all the awesome stuff included in Ruby and in ecosystem
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Chapter 30. Files
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Ruby on Rails
Develop web applications with ease.
58
Chapter 31. Introduction
59