Method: ActiveSupport::Testing::Assertions#assert_no_changes

Defined in:
activesupport/lib/active_support/testing/assertions.rb

#assert_no_changes(expression, message = nil, from: UNTRACKED, &block) ⇒ Object

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

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

Provide the optional keyword argument :from to specify the expected initial value.

assert_no_changes -> { Status.all_good? }, from: true 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



252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
 
# File 'activesupport/lib/active_support/testing/assertions.rb', line 252

def assert_no_changes(expression, message = nil, from: UNTRACKED, &block)
  exp = expression.respond_to?(:call) ? expression : -> { eval(expression.to_s, block.binding) }

  before = exp.call
  retval = _assert_nothing_raised_or_warn("assert_no_changes", &block)

  unless from == UNTRACKED
    rich_message = -> do
      error = "Expected initial value of #{from.inspect}, got #{before.inspect}"
      error = "#{message}.\n#{error}" if message
      error
    end
    assert from === before, rich_message
  end

  after = exp.call

  rich_message = -> do
    code_string = expression.respond_to?(:call) ? _callable_to_source_string(expression) : expression
    error = "`#{code_string}` changed"
    error = "#{message}.\n#{error}" if message
    error
  end

  if before.nil?
    assert_nil after, rich_message
  else
    assert_equal before, after, rich_message
  end

  retval
end