[Fix #289] don't count assertions twice when their return value is being assigned

changelog/fix_don_t_count_assertions_twice_when_their.md

@@ -0,0 +1 @@
+* [#289](https://github.com/rubocop/rubocop-minitest/issues/289): Don't count assertions twice when their return value is being assigned. ([@G-Rath][])

lib/rubocop/cop/minitest/multiple_assertions.rb

@@ -53,22 +53,27 @@ def on_class(class_node)
         def assertions_count(node)
           return 0 unless node.is_a?(RuboCop::AST::Node)
 
-          assertions =
-            case node.type
-            when :if, :case, :case_match
-              assertions_count_in_branches(node.branches)
-            when :rescue
-              assertions_count(node.body) + assertions_count_in_branches(node.branches)
-            when :block, :numblock
-              assertions_count(node.body)
-            else
-              node.each_child_node.sum { |child| assertions_count(child) }
-            end
-
+          assertions = assertions_count_based_on_type(node)
           assertions += 1 if assertion_method?(node)
           assertions
         end
 
+        def assertions_count_based_on_type(node)
+          case node.type
+          when :if, :case, :case_match
+            assertions_count_in_branches(node.branches)
+          when :rescue
+            assertions_count(node.body) + assertions_count_in_branches(node.branches)
+          when :block, :numblock
+            assertions_count(node.body)
+          when *RuboCop::AST::Node::ASSIGNMENTS
+            # checking assignment bodies is handled by assertion_method?
+            0
+          else
+            node.each_child_node.sum { |child| assertions_count(child) }
+          end
+        end
+
         def assertions_count_in_branches(branches)
           branches.map { |branch| assertions_count(branch) }.max
         end

test/rubocop/cop/minitest/multiple_assertions_test.rb

@@ -113,6 +113,33 @@ def test_asserts_once
     RUBY
   end
 
+  def test_assignments_are_not_counted_twice
+    assert_no_offenses(<<~RUBY)
+      class FooTest < Minitest::Test
+        def test_asserts_once
+          _ = assert_equal(1, 2)
+        end
+      end
+    RUBY
+  end
+
+  def test_assignments_are_not_counted_complex
+    assert_offense(<<~RUBY)
+      class FooTest < ActiveSupport::TestCase
+        test "#render errors include stack traces" do
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Test case has too many assertions [3/1].
+          err = assert_raises React::ServerRendering::PrerenderError do
+            @renderer.render("NonExistentComponent", {}, nil)
+          end
+
+          assert_match(/NonExistentComponent/, err.to_s, "it names the component")
+
+          assert_match(/\n/, err.to_s, "it includes the multi-line backtrace")
+        end
+      end
+    RUBY
+  end
+
   def test_does_not_register_offense_when_using_or_assigning_a_value_to_an_object_attribute
     assert_no_offenses(<<~RUBY)
       class FooTest < Minitest::Test
@@ -125,6 +152,19 @@ def test_asserts_once
     RUBY
   end
 
+  def test_does_not_register_offense_when_using_or_assigning_an_assertion_return_value_to_an_object_attribute
+    assert_offense(<<~RUBY)
+      class FooTest < Minitest::Test
+        def test_asserts_once
+        ^^^^^^^^^^^^^^^^^^^^^ Test case has too many assertions [2/1].
+          var ||= assert_equal(1, 2)
+
+          assert_equal(foo, bar)
+        end
+      end
+    RUBY
+  end
+
   def test_generates_a_todo_based_on_the_worst_violation
     inspect_source(<<-RUBY, @cop, 'test/foo_test.rb')
       class FooTest < Minitest::Test