Conditional Tests

Introduction

When defining type-parameterized tests, it's common for individual test cases to have stricter requirements on the type parameter than the actual subject of the tests. For example, a container type may have equality operators if and only if the value type also has equality operators. To get full test coverage these conditional features need to be fully tested, but they do not compile for certain values of the type parameter, and Google Test does not provide any built-in way to conditionally exclude them. This header provides macros which allow test cases to be conditionally included or excluded depending on the type parameter.

Macros

The test macro CONDITIONAL_TYPED_TEST_P works like TYPED_TEST_P from Google Test but with a third argument for a condition depending on TypeParam. The third argument is variadic within the preprocessor so it should not be necessary to parenthesize more complicated template conditions. Here is an example:

// Declare the typed test suite as normal
TYPED_TEST_SUITE_P(MySuite);
 
// Unconditional test
TYPED_TEST_P(MySuite, TestCase1) {
  EXPECT_EQ(some_class<TypeParam>{}, 0);
}
 
// Conditional test
CONDITIONAL_TYPED_TEST_P(MySuite, TestCase2, std::is_default_constructible<TypeParam>::value) {
  EXPECT_EQ(some_class<TypeParam>::default_value, TypeParam{});
}
 
// Register the conditional tests exactly as you would with a normal unconditional test
REGISTER_TYPED_TEST_SUITE_P(MySuite, TestCase1, TestCase2);

The conditional type test will run with the given body when TypeParam is default-constructible, and will run with an empty body when TypeParam is not default-constructible. In the latter case, the test body is never instantiated, so it's possible to write tests which fail to compile when the condition does not hold.