AssertKindOf: also replace is_a? as well

lib/rubocop/cop/minitest/assert_kind_of.rb

@@ -11,14 +11,22 @@ module Minitest
       #   assert(object.kind_of?(Class))
       #   assert(object.kind_of?(Class), 'message')
       #
+      #   # bad
+      #   # `#is_a?` is an alias for `#kind_of?
+      #   assert(object.is_a?(Class))
+      #   assert(object.is_a?(Class), 'message')
+      #
       #   # good
       #   assert_kind_of(Class, object)
       #   assert_kind_of(Class, object, 'message')
       #
       class AssertKindOf < Base
         extend MinitestCopRule
 
-        define_rule :assert, target_method: :kind_of?, inverse: true
+        define_rule :assert,
+          target_method: [:kind_of?, :is_a?],
+          preferred_method: :assert_kind_of,
+          inverse: true
       end
     end
   end

test/rubocop/cop/minitest/assert_kind_of_test.rb

@@ -22,6 +22,26 @@ def test_do_something
     RUBY
   end
 
+
+  def test_registers_offense_when_using_assert_with_is_a
+    assert_offense(<<~RUBY)
+      class FooTest < Minitest::Test
+        def test_do_something
+          assert(object.is_a?(SomeClass))
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer using `assert_kind_of(SomeClass, object)`.
+        end
+      end
+    RUBY
+
+    assert_correction(<<~RUBY)
+      class FooTest < Minitest::Test
+        def test_do_something
+          assert_kind_of(SomeClass, object)
+        end
+      end
+    RUBY
+  end
+
   def test_registers_offense_when_using_assert_with_kind_of_and_message
     assert_offense(<<~RUBY)
       class FooTest < Minitest::Test
@@ -41,6 +61,25 @@ def test_do_something
     RUBY
   end
 
+  def test_registers_offense_when_using_assert_with_is_a_and_message
+    assert_offense(<<~RUBY)
+      class FooTest < Minitest::Test
+        def test_do_something
+          assert(object.is_a?(SomeClass), 'message')
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer using `assert_kind_of(SomeClass, object, 'message')`.
+        end
+      end
+    RUBY
+
+    assert_correction(<<~RUBY)
+      class FooTest < Minitest::Test
+        def test_do_something
+          assert_kind_of(SomeClass, object, 'message')
+        end
+      end
+    RUBY
+  end
+
   def test_does_not_register_offense_when_using_assert_kind_of_method
     assert_no_offenses(<<~RUBY)
       class FooTest < Minitest::Test