[Fix #187] Fix an error for Minitest/EmptyLineBeforeAssertionMethods

Fixes #187.

This PR fixes an error for `Minitest/EmptyLineBeforeAssertionMethods`
when using method call with block.

changelog/fix_an_error_for_minitest_empty_line_before_assertion_methods.md

@@ -0,0 +1 @@
+* [#187](https://github.com/rubocop/rubocop-minitest/issues/187): Fix an error for `Minitest/EmptyLineBeforeAssertionMethods` when using method call with block. ([@koic][])

lib/rubocop/cop/minitest/empty_line_before_assertion_methods.rb

@@ -25,6 +25,7 @@ class EmptyLineBeforeAssertionMethods < Base
         def on_send(node)
           return unless assertion_method?(node)
           return unless (previous_line_node = node.left_sibling)
+          return unless previous_line_node.is_a?(RuboCop::AST::Node)
           return if accept_previous_line?(previous_line_node, node)
 
           previous_line_node = previous_line_node.arguments.last if use_heredoc_argument?(previous_line_node)

test/rubocop/cop/minitest/empty_line_before_assertion_methods_test.rb

@@ -89,6 +89,26 @@ def test_do_something
     RUBY
   end
 
+  def test_registers_offense_when_using_method_call_with_block_arg_before_assertion_method
+    assert_offense(<<~RUBY)
+      def test_do_something
+        block = -> { raise CustomError, 'This is really bad' }
+        error = assert_raises(CustomError, &block)
+        assert_equal 'This is really bad', error.message
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Add empty line before assertion.
+      end
+    RUBY
+
+    assert_correction(<<~RUBY)
+      def test_do_something
+        block = -> { raise CustomError, 'This is really bad' }
+        error = assert_raises(CustomError, &block)
+
+        assert_equal 'This is really bad', error.message
+      end
+    RUBY
+  end
+
   def test_does_not_register_offense_when_using_empty_line_before_assertion_methods
     assert_no_offenses(<<~RUBY)
       def test_do_something