Constexpr Test Macros

Introduction

Arene Base provides a unit testing support library, compatible with gtest, which provides CONSTEXPR_TEST and CONSTEXPR_TYPED_TEST macros which mirror the TEST and TYPED_TEST macros defined by GoogleTest. These macros provide an alternative approach to using STATIC_ASSERT_XXXmacros when compile-time tests. Additionally, this support library provides CONSTEXPR_ASSERT, an assertion macro that replaces ones from GoogleTest.

The constexpr test macros invoke the function body at compile-time. Function bodies are also invoked at runtime to allow generation of coverage.

Usage

Here is a simple example of changing a runtime evaluated test using TEST to a compile-time test using CONSTEXPR_TEST.

TEST(ConstexprContainer, PushPlacesTheElementAtFront)
{
  constexpr_container<int> container;
  for (auto value : {1, 2, 3, 4})
  {
    container.push(value);
    ASSERT_EQ(container.front(), value);
  }
}

CONSTEXPR_TEST(ConstexprContainer, PushPlacesTheElementAtFront)
{
  constexpr_container<int> container;
  for (auto value: {1, 2, 3, 4})
  {
    container.push(value);
    CONSTEXPR_ASSERT(container.front() == value);
  }
}

GoogleTest assertion macros (e.g. ASSERT_EQ) cannot be used within a CONSTEXPR_TEST. Instead, a single CONSTEXPR_ASSERT assertion macro is available.

Use of CONSTEXPR_TYPED_TEST is analogous to CONSTEXPR_TEST.

CONSTEXPR_TYPED_TEST(ConstexprContainer, PushPlacesTheElementAtFront)
{
  constexpr_container<TypeParam> container;
  for (auto value: {1, 2, 3, 4})
  {
    container.push(value);
    CONSTEXPR_ASSERT(container.front() == value);
  }
}

Limitations

As the test bodies of CONSTEXPR_TEST and CONSTEXPR_TYPED_TEST must be invocable at compile-time, they cannot refer to non-constexpr values. This includes the this pointer to the test fixture.