Make Minitest/AssertEqual aware of assert_operator

This PR makes `Minitest/AssertEqual` aware of `assert_operator`.

changelog/new_make_minitest_assert_equal_aware_of_assert_operator.md

@@ -0,0 +1 @@
+* [#266](https://github.com/rubocop/rubocop-minitest/pull/266): Make `Minitest/AssertEqual` aware of `assert_operator`. ([@koic][])

lib/rubocop/cop/minitest/assert_equal.rb

@@ -9,14 +9,46 @@ module Minitest
       # @example
       #   # bad
       #   assert("rubocop-minitest" == actual)
+      #   assert_operator("rubocop-minitest", :==, actual)
       #
       #   # good
       #   assert_equal("rubocop-minitest", actual)
       #
       class AssertEqual < Base
-        extend MinitestCopRule
+        include ArgumentRangeHelper
+        extend AutoCorrector
 
-        define_rule :assert, target_method: :==, preferred_method: :assert_equal
+        MSG = 'Prefer using `assert_equal(%<preferred>s)`.'
+        RESTRICT_ON_SEND = %i[assert assert_operator].freeze
+
+        def_node_matcher :assert_equal, <<~PATTERN
+          {
+            (send nil? :assert (send $_ :== $_) $...)
+            (send nil? :assert_operator $_ (sym :==) $_ $...)
+          }
+        PATTERN
+
+        # rubocop:disable Metrics/AbcSize
+        def on_send(node)
+          assert_equal(node) do |expected, actual, rest_args|
+            basic_arguments = "#{expected.source}, #{actual.source}"
+            preferred = (message_arg = rest_args.first) ? "#{basic_arguments}, #{message_arg.source}" : basic_arguments
+            message = format(MSG, preferred: preferred)
+
+            add_offense(node, message: message) do |corrector|
+              corrector.replace(node.loc.selector, 'assert_equal')
+
+              range = if node.method?(:assert)
+                        node.first_argument
+                      else
+                        node.first_argument.source_range.begin.join(node.arguments[2].source_range.end)
+                      end
+
+              corrector.replace(range, basic_arguments)
+            end
+          end
+        end
+        # rubocop:enable Metrics/AbcSize
       end
     end
   end

test/rubocop/cop/minitest/assert_equal_test.rb

@@ -104,20 +104,39 @@ def test_do_something
     RUBY
   end
 
-  def test_registers_offense_when_using_assert_with_equal_in_redundant_parentheses
+  def test_registers_offense_when_using_assert_operator_with_equal_symbol_argument
     assert_offense(<<~RUBY)
       class FooTest < Minitest::Test
         def test_do_something
-          assert(('rubocop-minitest' == actual))
-          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer using `assert_equal('rubocop-minitest', actual)`.
+          assert_operator('rubocop-minitest', :==, actual)
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer using `assert_equal('rubocop-minitest', actual)`.
+        end
+      end
+    RUBY
+
+    assert_correction(<<~RUBY)
+      class FooTest < Minitest::Test
+        def test_do_something
+          assert_equal('rubocop-minitest', actual)
+        end
+      end
+    RUBY
+  end
+
+  def test_registers_offense_when_using_assert_operator_with_equal_symbol_and_message_argument
+    assert_offense(<<~RUBY)
+      class FooTest < Minitest::Test
+        def test_do_something
+          assert_operator('rubocop-minitest', :==, actual, message)
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer using `assert_equal('rubocop-minitest', actual, message)`.
         end
       end
     RUBY
 
     assert_correction(<<~RUBY)
       class FooTest < Minitest::Test
         def test_do_something
-          assert_equal(('rubocop-minitest', actual))
+          assert_equal('rubocop-minitest', actual, message)
         end
       end
     RUBY
@@ -133,6 +152,27 @@ def test_do_something
     RUBY
   end
 
+  def test_registers_offense_when_using_assert_operator_with_negated_equal_symbol_argument
+    assert_no_offenses(<<~RUBY)
+      class FooTest < Minitest::Test
+        def test_do_something
+          assert_operator('rubocop-minitest', :!=, actual)
+        end
+      end
+    RUBY
+  end
+
+  # Redundant parentheses should be removed in another cop.
+  def test_does_not_register_offense_when_using_assert_with_equal_in_redundant_parentheses
+    assert_no_offenses(<<~RUBY)
+      class FooTest < Minitest::Test
+        def test_do_something
+          assert(('rubocop-minitest' == actual))
+        end
+      end
+    RUBY
+  end
+
   # See: https://github.com/rubocop/rubocop-minitest/issues/113
   def test_does_not_register_offense_when_assert_with_block_argument
     assert_no_offenses(<<~RUBY)