Fix raise error when usgin assert with block

changelog/fix_raise_error_using_assert_with_block.md

@@ -0,0 +1 @@
+* [#175](https://github.com/rubocop/rubocop-minitest/pull/175): Fix raise error when using assert with block. ([@ippachi][])

lib/rubocop/cop/mixin/predicate_assertion_handleable.rb

@@ -13,8 +13,9 @@ def on_send(node)
 
           first_argument = arguments.first
 
+          return unless first_argument
           return if first_argument.block_type? || first_argument.numblock_type?
-          return unless first_argument.respond_to?(:predicate_method?) && first_argument.predicate_method?
+          return unless predicate_method?(first_argument)
           return unless first_argument.arguments.count.zero?
 
           add_offense(node, message: offense_message(arguments)) do |corrector|
@@ -38,6 +39,10 @@ def peel_redundant_parentheses_from(arguments)
           peel_redundant_parentheses_from(arguments.first.children)
         end
 
+        def predicate_method?(first_argument)
+          first_argument.respond_to?(:predicate_method?) && first_argument.predicate_method?
+        end
+
         def offense_message(arguments)
           message_argument = arguments.last if arguments.first != arguments.last
 

test/rubocop/cop/minitest/assert_predicate_test.rb

@@ -152,4 +152,14 @@ def test_do_something
       end
     RUBY
   end
+
+  def test_does_not_raise_error_using_assert_with_block
+    assert_no_offenses(<<~RUBY)
+      class FooTest < Minitest::Test
+        def test_do_something
+          assert { true }
+        end
+      end
+    RUBY
+  end
 end