Module: AssertDifference

Defined in:
lib/assert_difference.rb

Overview

Copyright © 2010, 2011, 2012 José Pablo Fernández

Constant Summary collapse

VERSION = 
"0.4.2"

Instance Method Summary collapse

Instance Method Details

#assert_difference(expressions, difference = 1, message = nil, &block) ⇒ Object

Test numeric difference between the return value of an expression as a result of what is evaluated in the yielded block.

assert_difference "Article.count" do
  post :create, :article => {...}
end

An arbitrary expression is passed in and evaluated.

assert_difference "assigns(:article).comments(:reload).size" do
  post :create, :comment => {...}
end

An arbitrary positive or negative difference can be specified. The default is +1.

assert_difference "Article.count", -1 do
  post :delete, :id => ...
end

An array of expressions can also be passed in and evaluated.

assert_difference [ "Article.count", "Post.count" ], +2 do
  post :create, :article => {...}
end

A error message can be specified.

assert_difference "Article.count", -1, "An Article should be destroyed" do
  post :delete, :id => ...
end

Various assertions can be combined into one, instead of writing:

assert_difference "Company.count" do
  assert_difference "User.count", +5 do
    assert_difference "Article.count", -1 do
      post :something
    end
  end
end

you can now write:

assert_difference "Article.count" => 1, "assigns(:article).comments(:reload).size" => 1, "Article.count" => -1 do
  post :something
end

the results of the block is the result of the assert, so you can write

email = assert_difference "ActionMailer::Base.deliveries.count" => +1 do
    Mailer.reset_password_email(@user).deliver
end
assert_equal [@user.email], email.to

Parameters:

  • expressions (Array, Hash) —

    array of expressions to evaluate or hash table of expressions and expected difference.

  • difference (Integer) (defaults to: 1) —

    expected difference when using an array or single expression.

  • message (String, nil) (defaults to: nil) —

    error message to display. One would be constructed if nil.

Returns:

  • whatever the block returned



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# File 'lib/assert_difference.rb', line 66

def assert_difference(expressions, difference = 1, message = nil, &block)
  b = block.send(:binding)
  if !expressions.is_a? Hash
    exps = Array.wrap(expressions)
    expressions = {}
    exps.each { |e| expressions[e] = difference }
  end

  before = {}
  expressions.each { |exp, _| before[exp] = eval(exp, b) }

  result = yield

  error_messages = []
  expressions.each do |exp, diff|
    expected = before[exp] + diff
    actual = eval(exp, b)
    if expected != actual
      error = "#{exp.inspect} didn't change by #{diff} (expecting #{expected}, but got #{actual})"
      error = "#{message}.\n#{error}" if message
      error_messages << error
    end
  end

  if error_messages.any?
    fail error_messages.join(error_messages.any? { |m| m.include? "\n" } ? "\n\n" : ". ").strip
  end

  return result
end