catch2/docs/test-fixtures.md

Test fixtures

Defining test fixtures

Although Catch allows you to group tests together as sections within a test case, it can still be convenient, sometimes, to group them using a more traditional test fixture. Catch fully supports this too. You define the test fixture as a simple structure:

class UniqueTestsFixture {
  private:
   static int uniqueID;
  protected:
   DBConnection conn;
  public:
   UniqueTestsFixture() : conn(DBConnection::createConnection("myDB")) {
   }
  protected:
   int getID() {
     return ++uniqueID;
   }
 };

 int UniqueTestsFixture::uniqueID = 0;

 TEST_CASE_METHOD(UniqueTestsFixture, "Create Employee/No Name", "[create]") {
   REQUIRE_THROWS(conn.executeSQL("INSERT INTO employee (id, name) VALUES (?, ?)", getID(), ""));
 }
 TEST_CASE_METHOD(UniqueTestsFixture, "Create Employee/Normal", "[create]") {
   REQUIRE(conn.executeSQL("INSERT INTO employee (id, name) VALUES (?, ?)", getID(), "Joe Bloggs"));
 }

The two test cases here will create uniquely-named derived classes of UniqueTestsFixture and thus can access the getID() protected method and conn member variables. This ensures that both the test cases are able to create a DBConnection using the same method (DRY principle) and that any ID's created are unique such that the order that tests are executed does not matter.

Catch2 also provides TEMPLATE_TEST_CASE_METHOD and TEMPLATE_PRODUCT_TEST_CASE_METHOD that can be used together with templated fixtures and templated template fixtures to perform tests for multiple different types. Unlike TEST_CASE_METHOD, TEMPLATE_TEST_CASE_METHOD and TEMPLATE_PRODUCT_TEST_CASE_METHOD do require the tag specification to be non-empty, as it is followed by further macro arguments.

Also note that, because of limitations of the C++ preprocessor, if you want to specify a type with multiple template parameters, you need to enclose it in parentheses, e.g. std::map<int, std::string> needs to be passed as (std::map<int, std::string>). In the case of TEMPLATE_PRODUCT_TEST_CASE_METHOD, if a member of the type list should consist of more than single type, it needs to be enclosed in another pair of parentheses, e.g. (std::map, std::pair) and ((int, float), (char, double)).

Example:

template< typename T >
struct Template_Fixture {
    Template_Fixture(): m_a(1) {}

    T m_a;
};

TEMPLATE_TEST_CASE_METHOD(Template_Fixture,
                          "A TEMPLATE_TEST_CASE_METHOD based test run that succeeds",
                          "[class][template]",
                          int, float, double) {
    REQUIRE( Template_Fixture<TestType>::m_a == 1 );
}

template<typename T>
struct Template_Template_Fixture {
    Template_Template_Fixture() {}

    T m_a;
};

template<typename T>
struct Foo_class {
    size_t size() {
        return 0;
    }
};

TEMPLATE_PRODUCT_TEST_CASE_METHOD(Template_Template_Fixture,
                                  "A TEMPLATE_PRODUCT_TEST_CASE_METHOD based test succeeds",
                                  "[class][template]",
                                  (Foo_class, std::vector),
                                  int) {
    REQUIRE( Template_Template_Fixture<TestType>::m_a.size() == 0 );
}

While there is an upper limit on the number of types you can specify in single TEMPLATE_TEST_CASE_METHOD or TEMPLATE_PRODUCT_TEST_CASE_METHOD, the limit is very high and should not be encountered in practice.

Signature-based parametrised test fixtures

Introduced in Catch2 2.8.0.

Catch2 also provides TEMPLATE_TEST_CASE_METHOD_SIG and TEMPLATE_PRODUCT_TEST_CASE_METHOD_SIG to support fixtures using non-type template parameters. These test cases work similar to TEMPLATE_TEST_CASE_METHOD and TEMPLATE_PRODUCT_TEST_CASE_METHOD, with additional positional argument for signature.

Example:

template <int V>
struct Nttp_Fixture{
    int value = V;
};

TEMPLATE_TEST_CASE_METHOD_SIG(
    Nttp_Fixture,
    "A TEMPLATE_TEST_CASE_METHOD_SIG based test run that succeeds",
    "[class][template][nttp]",
    ((int V), V),
    1, 3, 6) {
    REQUIRE(Nttp_Fixture<V>::value > 0);
}

template<typename T>
struct Template_Fixture_2 {
    Template_Fixture_2() {}

    T m_a;
};

template< typename T, size_t V>
struct Template_Foo_2 {
    size_t size() { return V; }
};

TEMPLATE_PRODUCT_TEST_CASE_METHOD_SIG(
    Template_Fixture_2, 
    "A TEMPLATE_PRODUCT_TEST_CASE_METHOD_SIG based test run that succeeds", 
    "[class][template][product][nttp]", 
    ((typename T, size_t S), T, S),
    (std::array, Template_Foo_2),
    ((int,2), (float,6))) {
    REQUIRE(Template_Fixture_2<TestType>{}.m_a.size() >= 2);
}

Template fixtures with types specified in template type lists

Catch2 also provides TEMPLATE_LIST_TEST_CASE_METHOD to support template fixtures with types specified in template type lists like std::tuple, boost::mpl::list or boost::mp11::mp_list. This test case works the same as TEMPLATE_TEST_CASE_METHOD, only difference is the source of types. This allows you to reuse the template type list in multiple test cases.

Example:

using MyTypes = std::tuple<int, char, double>;
TEMPLATE_LIST_TEST_CASE_METHOD(Template_Fixture,
                               "Template test case method with test types specified inside std::tuple",
                               "[class][template][list]",
                               MyTypes) {
    REQUIRE( Template_Fixture<TestType>::m_a == 1 );
}

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