Warning if invocation matches never expectation

Currently when an invocation matches an expectation which does not allow
invocations (i.e. `Expectation#never` has been called on it), but the
invocation also matches another expectation which does allow
invocations, then the test does not fail with an unexpected invocation
error.

In #679 I'm planning to change this behaviour so the test fails fast
with an unexpected invocation error. This commit displays a deprecation
warning instead to give users a chance to update their code before the
actual change is made.

lib/mocha/mock.rb

@@ -8,6 +8,7 @@
 require 'mocha/parameters_matcher'
 require 'mocha/argument_iterator'
 require 'mocha/expectation_error_factory'
+require 'mocha/deprecation'
 
 module Mocha
   # Traditional mock object.
@@ -323,9 +324,13 @@ def handle_method_call(symbol, arguments, block)
       invocation = Invocation.new(self, symbol, arguments, block)
 
       matching_expectation_allowing_invocation = all_expectations.match_allowing_invocation(invocation)
+      matching_expectation_never_allowing_invocation = all_expectations.match_never_allowing_invocation(invocation)
       matching_expectation_ignoring_order = all_expectations.match(invocation, ignoring_order: true)
 
       if matching_expectation_allowing_invocation
+        if matching_expectation_never_allowing_invocation
+          invocation_not_allowed_warning(invocation, matching_expectation_never_allowing_invocation)
+        end
         matching_expectation_allowing_invocation.invoke(invocation)
       elsif matching_expectation_ignoring_order || (!matching_expectation_ignoring_order && !@everything_stubbed)
         raise_unexpected_invocation_error(invocation, matching_expectation_ignoring_order)
@@ -373,6 +378,15 @@ def any_expectations?
 
     private
 
+    def invocation_not_allowed_warning(invocation, expectation)
+      messages = [
+        "The expectation defined at #{expectation.definition_location} does not allow invocations.",
+        "However, #{invocation.call_description} was invoked.",
+        'This invocation will cause the test to fail fast in a future version of Mocha.'
+      ]
+      Deprecation.warning(messages.join(' '))
+    end
+
     def raise_unexpected_invocation_error(invocation, matching_expectation)
       if @unexpected_invocation.nil?
         @unexpected_invocation = invocation

test/acceptance/mocked_methods_dispatch_test.rb

@@ -1,4 +1,6 @@
 require File.expand_path('../acceptance_test_helper', __FILE__)
+require 'deprecation_disabler'
+require 'execution_point'
 
 class MockedMethodDispatchTest < Mocha::TestCase
   include AcceptanceTest
@@ -72,4 +74,25 @@ def test_should_find_latest_expectation_with_range_of_expected_invocation_count_
     end
     assert_passed(test_result)
   end
+
+  def test_should_fail_fast_if_invocation_matches_expectation_with_never_cardinality
+    execution_point = nil
+    test_result = run_as_test do
+      mock = mock('mock')
+      mock.stubs(:method)
+      mock.expects(:method).never; execution_point = ExecutionPoint.current
+      DeprecationDisabler.disable_deprecations do
+        mock.method
+      end
+    end
+    assert_passed(test_result)
+    message = Mocha::Deprecation.messages.last
+    location = execution_point.location
+    expected = [
+      "The expectation defined at #{location} does not allow invocations.",
+      'However, #<Mock:mock>.method() was invoked.',
+      'This invocation will cause the test to fail fast in a future version of Mocha.'
+    ]
+    assert_equal expected.join(' '), message
+  end
 end