Google Test: Parameterized tests which use an existing test fixture class?

Question

I have a test fixture class which is currently used by many tests.

#include <gtest/gtest.h>
class MyFixtureTest : public ::testing::Test {
  void SetUp() { ... }
};

I would like to create a parameterized test which also uses all that MyFixtureTest has to offer, without needing to change all my existing tests.

How do I do that?

I have found similar discussions on the web, but have not fully understood their answers.

Answer 1

The problem is that for regular tests your fixture has to be derived from testing::Test and for parameterized tests, it has to be derived from testing::TestWithParam<>.

In order to accommodate that, you'll have to modify your fixture class in order to work with your parameter type

template <class T> class MyFixtureBase : public T {
  void SetUp() { ... };
  // Put the rest of your original MyFixtureTest here.
};

// This will work with your non-parameterized tests.
class MyFixtureTest : public MyFixtureBase<testing::Test> {};

// This will be the fixture for all your parameterized tests.
// Just substitute the actual type of your parameters for MyParameterType.
class MyParamFixtureTest : public MyFixtureBase<
    testing::TestWithParam<MyParameterType> > {};

This way you can keep all your existing tests intact while creating parameterized tests using

TEST_P(MyParamFixtureTest, MyTestName) { ... }

Answer 2

This question is now answered in the Google Test documentation (the answer from VladLosev is technically correct, but perhaps slightly more work)

Specifically, when you want to add parameters to a pre-existing fixture class, you can do

class MyFixtureTest : public ::testing::Test {
  ...
};
class MyParamFixtureTest : public MyFixtureTest,
                           public ::testing::WithParamInterface<MyParameterType> {
  ...
};

TEST_P(MyParamFixtureTest, MyTestName) { ... }

Answer 3

If you create a new fixture that is derived from this common one and than create your parameterized tests on that derived class - would that help you and solve your problem?

From Google Test wiki page: "In Google Test, you share a fixture among test cases by putting the shared logic in a base test fixture, then deriving from that base a separate fixture for each test case that wants to use this common logic."