Include a Cop to enforce refute(actual) over assert_equal(false)

This commit adds a Cop that checks some usage of
`assert_equal(false, something)` and enforces the usage of
`refute(something)` instead.

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## master (unreleased)
 
+* [#18](https://github.com/rubocop-hq/rubocop-minitest/pull/18): Add new `Minitest/RefuteFalse` cop. ([@duduribeiro][])
+
 ## 0.2.1 (2019-09-24)
 
 ### Bug fixes

config/default.yml

@@ -31,3 +31,9 @@ Minitest/RefuteNil:
   StyleGuide: 'https://github.com/rubocop-hq/minitest-style-guide#refute-nil'
   Enabled: true
   VersionAdded: '0.2'
+
+Minitest/RefuteFalse:
+  Description: 'Check if your test uses `refute(actual)` instead of `assert_equal(false, actual)`.'
+  StyleGuide: 'https://github.com/rubocop-hq/minitest-style-guide#refute-false'
+  Enabled: true
+  VersionAdded: '0.3'

lib/rubocop/cop/minitest/refute_false.rb

@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Minitest
+      # Check if your test uses `refute(actual)`
+      # instead of `assert_equal(false, actual)`.
+      #
+      # @example
+      #   # bad
+      #   assert_equal(false, actual)
+      #   assert_equal(false, actual, 'the message')
+      #
+      #   # good
+      #   refute(actual)
+      #   refute(actual, 'the message')
+      #
+      class RefuteFalse < Cop
+        MSG = 'Prefer using `refute(%<arguments>s)` over ' \
+              '`assert_equal(false, %<arguments>s)`.'
+
+        def_node_matcher :assert_equal_with_false, <<~PATTERN
+          (send nil? :assert_equal false $_ $...)
+        PATTERN
+
+        def on_send(node)
+          assert_equal_with_false(node) do |actual, rest_receiver_arg|
+            message = rest_receiver_arg.first
+
+            arguments = [actual.source, message&.source].compact.join(', ')
+
+            add_offense(node, message: format(MSG, arguments: arguments))
+          end
+        end
+
+        def autocorrect(node)
+          lambda do |corrector|
+            arguments = node.arguments.reject(&:false_type?)
+            replacement = arguments.map(&:source).join(', ')
+            corrector.replace(node.loc.expression, "refute(#{replacement})")
+          end
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/minitest_cops.rb

@@ -4,4 +4,5 @@
 require_relative 'minitest/assert_nil'
 require_relative 'minitest/assert_includes'
 require_relative 'minitest/assert_truthy'
+require_relative 'minitest/refute_false'
 require_relative 'minitest/refute_nil'

manual/cops.md

@@ -5,6 +5,7 @@
 * [Minitest/AssertIncludes](cops_minitest.md#minitestassertincludes)
 * [Minitest/AssertNil](cops_minitest.md#minitestassertnil)
 * [Minitest/AssertTruthy](cops_minitest.md#minitestasserttruthy)
+* [Minitest/RefuteFalse](cops_minitest.md#minitestrefutefalse)
 * [Minitest/RefuteNil](cops_minitest.md#minitestrefutenil)
 
 <!-- END_COP_LIST -->

manual/cops_minitest.md

@@ -98,6 +98,31 @@ assert(actual, 'the message')
 
 * [https://github.com/rubocop-hq/minitest-style-guide#assert-truthy](https://github.com/rubocop-hq/minitest-style-guide#assert-truthy)
 
+## Minitest/RefuteFalse
+
+Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+--- | --- | --- | --- | ---
+Enabled | Yes | Yes  | 0.3 | -
+
+Check if your test uses `refute(actual)`
+instead of `assert_equal(false, actual)`.
+
+### Examples
+
+```ruby
+# bad
+assert_equal(false, actual)
+assert_equal(false, actual, 'the message')
+
+# good
+refute(actual)
+refute(actual, 'the message')
+```
+
+### References
+
+* [https://github.com/rubocop-hq/minitest-style-guide#refute-false](https://github.com/rubocop-hq/minitest-style-guide#refute-false)
+
 ## Minitest/RefuteNil
 
 Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged

test/rubocop/cop/minitest/refute_false_test.rb

@@ -0,0 +1,120 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class RefuteFalseTest < Minitest::Test
+  def setup
+    @cop = RuboCop::Cop::Minitest::RefuteFalse.new
+  end
+
+  def test_registers_offense_when_using_assert_equal_with_false
+    assert_offense(<<~RUBY, @cop)
+      class FooTest < Minitest::Test
+        def test_do_something
+          assert_equal(false, somestuff)
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer using `refute(somestuff)` over `assert_equal(false, somestuff)`.
+        end
+      end
+    RUBY
+
+    assert_correction(<<~RUBY, @cop)
+      class FooTest < Minitest::Test
+        def test_do_something
+          refute(somestuff)
+        end
+      end
+    RUBY
+  end
+
+  def test_registers_offense_when_using_assert_equal_with_false_and_message
+    assert_offense(<<~RUBY, @cop)
+      class FooTest < Minitest::Test
+        def test_do_something
+          assert_equal(false, somestuff, 'the message')
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer using `refute(somestuff, 'the message')` over `assert_equal(false, somestuff, 'the message')`.
+        end
+      end
+    RUBY
+
+    assert_correction(<<~RUBY, @cop)
+      class FooTest < Minitest::Test
+        def test_do_something
+          refute(somestuff, 'the message')
+        end
+      end
+    RUBY
+  end
+
+  def test_registers_offense_when_using_assert_equal_with_method_call
+    assert_offense(<<~RUBY, @cop)
+      class FooTest < Minitest::Test
+        def test_do_something
+          assert_equal(false, obj.do_something, 'the message')
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer using `refute(obj.do_something, 'the message')` over `assert_equal(false, obj.do_something, 'the message')`.
+        end
+      end
+    RUBY
+
+    assert_correction(<<~RUBY, @cop)
+      class FooTest < Minitest::Test
+        def test_do_something
+          refute(obj.do_something, 'the message')
+        end
+      end
+    RUBY
+  end
+
+  def test_registers_offense_when_using_assert_equal_with_variable_message
+    assert_offense(<<~RUBY, @cop)
+      class FooTest < Minitest::Test
+        def test_do_something
+          message = 'the message'
+          assert_equal(false, somestuff, message)
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer using `refute(somestuff, message)` over `assert_equal(false, somestuff, message)`.
+        end
+      end
+    RUBY
+
+    assert_correction(<<~RUBY, @cop)
+      class FooTest < Minitest::Test
+        def test_do_something
+          message = 'the message'
+          refute(somestuff, message)
+        end
+      end
+    RUBY
+  end
+
+  def test_registers_offense_when_using_assert_equal_with_constant_message
+    assert_offense(<<~RUBY, @cop)
+      class FooTest < Minitest::Test
+        MESSAGE = 'the message'
+
+        def test_do_something
+          assert_equal(false, somestuff, MESSAGE)
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer using `refute(somestuff, MESSAGE)` over `assert_equal(false, somestuff, MESSAGE)`.
+        end
+      end
+    RUBY
+
+    assert_correction(<<~RUBY, @cop)
+      class FooTest < Minitest::Test
+        MESSAGE = 'the message'
+
+        def test_do_something
+          refute(somestuff, MESSAGE)
+        end
+      end
+    RUBY
+  end
+
+  def test_does_not_register_offense_when_using_refute_method
+    assert_no_offenses(<<~RUBY, @cop)
+      class FooTest < Minitest::Test
+        def test_do_something
+          refute(somestuff)
+        end
+      end
+    RUBY
+  end
+end