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Methods
A
Constants
UNTRACKED = Object.new
 
Instance Public methods
assert_changes(expression, message = nil, from: UNTRACKED, to: UNTRACKED, &block)

Assertion that the result of evaluating an expression is changed before and after invoking the passed in block.

assert_changes 'Status.all_good?' do
  post :create, params: { status: { ok: false } }
end

You can pass the block as a string to be evaluated in the context of the block. A lambda can be passed for the block as well.

assert_changes -> { Status.all_good? } do
  post :create, params: { status: { ok: false } }
end

The assertion is useful to test side effects. The passed block can be anything that can be converted to string with to_s.

assert_changes :@object do
  @object = 42
end

The keyword arguments :from and :to can be given to specify the expected initial value and the expected value after the block was executed.

assert_changes :@object, from: nil, to: :foo do
  @object = :foo
end

An error message can be specified.

assert_changes -> { Status.all_good? }, 'Expected the status to be bad' do
  post :create, params: { status: { incident: true } }
end
# File activesupport/lib/active_support/testing/assertions.rb, line 132
def assert_changes(expression, message = nil, from: UNTRACKED, to: UNTRACKED, &block)
  exp = expression.respond_to?(:call) ? expression : -> { eval(expression.to_s, block.binding) }

  before = exp.call
  retval = yield

  unless from == UNTRACKED
    error = "#{expression.inspect} isn't #{from}"
    error = "#{message}.\n#{error}" if message
    assert from === before, error
  end

  after = exp.call

  if to == UNTRACKED
    error = "#{expression.inspect} didn't changed"
    error = "#{message}.\n#{error}" if message
    assert_not_equal before, after, error
  else
    message = "#{expression.inspect} didn't change to #{to}"
    error = "#{message}.\n#{error}" if message
    assert to === after, error
  end

  retval
end
assert_difference(expression, difference = 1, message = nil, &block)

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, params: { article: {...} }
end

An arbitrary expression is passed in and evaluated.

assert_difference 'Article.last.comments(:reload).size' do
  post :create, params: { comment: {...} }
end

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

assert_difference 'Article.count', -1 do
  post :delete, params: { id: ... }
end

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

assert_difference [ 'Article.count', 'Post.count' ], 2 do
  post :create, params: { article: {...} }
end

A lambda or a list of lambdas can be passed in and evaluated:

assert_difference ->{ Article.count }, 2 do
  post :create, params: { article: {...} }
end

assert_difference [->{ Article.count }, ->{ Post.count }], 2 do
  post :create, params: { article: {...} }
end

An error message can be specified.

assert_difference 'Article.count', -1, 'An Article should be destroyed' do
  post :delete, params: { id: ... }
end
# File activesupport/lib/active_support/testing/assertions.rb, line 63
def assert_difference(expression, difference = 1, message = nil, &block)
  expressions = Array(expression)

  exps = expressions.map { |e|
    e.respond_to?(:call) ? e : lambda { eval(e, block.binding) }
  }
  before = exps.map(&:call)

  retval = yield

  expressions.zip(exps).each_with_index do |(code, e), i|
    error  = "#{code.inspect} didn't change by #{difference}"
    error  = "#{message}.\n#{error}" if message
    assert_equal(before[i] + difference, e.call, error)
  end

  retval
end
assert_no_changes(expression, message = nil, &block)

Assertion that the result of evaluating an expression is changed before and after invoking the passed in block.

assert_no_changes 'Status.all_good?' do
  post :create, params: { status: { ok: true } }
end

An error message can be specified.

assert_no_changes -> { Status.all_good? }, 'Expected the status to be good' do
  post :create, params: { status: { ok: false } }
end
# File activesupport/lib/active_support/testing/assertions.rb, line 171
def assert_no_changes(expression, message = nil, &block)
  exp = expression.respond_to?(:call) ? expression : -> { eval(expression.to_s, block.binding) }

  before = exp.call
  retval = yield
  after = exp.call

  error = "#{expression.inspect} did change to #{after}"
  error = "#{message}.\n#{error}" if message
  assert_equal before, after, error

  retval
end
assert_no_difference(expression, message = nil, &block)

Assertion that the numeric result of evaluating an expression is not changed before and after invoking the passed in block.

assert_no_difference 'Article.count' do
  post :create, params: { article: invalid_attributes }
end

An error message can be specified.

assert_no_difference 'Article.count', 'An Article should not be created' do
  post :create, params: { article: invalid_attributes }
end
# File activesupport/lib/active_support/testing/assertions.rb, line 94
def assert_no_difference(expression, message = nil, &block)
  assert_difference expression, 0, message, &block
end
assert_not(object, message = nil)

Asserts that an expression is not truthy. Passes if object is nil or false. “Truthy” means “considered true in a conditional” like if foo.

assert_not nil    # => true
assert_not false  # => true
assert_not 'foo'  # => Expected "foo" to be nil or false

An error message can be specified.

assert_not foo, 'foo should be false'
# File activesupport/lib/active_support/testing/assertions.rb, line 17
def assert_not(object, message = nil)
  message ||= "Expected #{mu_pp(object)} to be nil or false"
  assert !object, message
end