Only Verify Relevant Method Arguments

Tests become fragile when they expect exact values on irrelevant arguments.

Bad

TEST_F(DisplayGreetingTest, ShowSpecialGreetingOnNewYearsDay) {
  fake_clock_.SetTime(kNewYearsDay);
  fake_user_.SetName("Fake User");
  EXPECT_CALL(mock_user_prompter_,
              UpdatePrompt("Hi Fake User! Happy New Year!",
                           TitleBar("2018-01-01"), PromptStyle::kNormal));
  user_greeter_.DisplayGreeting();
}

• Only verify one behavior per test.
• Only verify arguments that affect the correctness of the specific behavior being tested.

Good

TEST_F(DisplayGreetingTest, ShowSpecialGreetingOnNewYearsDay) {
  fake_clock_.SetTime(kNewYearsDay);
  EXPECT_CALL(mock_user_prompter_,
              UpdatePrompt(HasSubstr("Happy New Year!"), _, _));
  user_greeter_.DisplayGreeting();
}

TEST_F(DisplayGreetingTest, RenderUserName) {
  fake_user_.SetName("Fake User");
  EXPECT_CALL(mock_user_prompter_, UpdatePrompt(HasSubstr("Fake User"), _, _));
  user_greeter_.DisplayGreeting();
}