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Write unit tests for C++ DLLs in Visual Studio

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There are several ways to test DLL code, depending on whether it exports the functions that you want to test. Choose one of the following ways:

The unit tests call only functions that are exported from the DLL: Add a separate test project as described in Write unit tests for C/C++. In the test project, add a reference to the DLL project.

Go to the procedure To reference exported functions from the DLL project.

The DLL is built as an .exe file: Add a separate test project. Link it to the output object file.

Go to the procedure To link the tests to the object or library files.

The unit tests call non-member functions that aren't exported from the DLL, and the DLL can be built as a static library: Change the DLL project so that it's compiled to a .lib file. Add a separate test project that references the project under test.

This approach has the benefit of allowing your tests to use non-exported members, but still keep the tests in a separate project.

Go to the procedure To change the DLL to a static library.

The unit tests must call non-member functions that aren't exported, and the code must be built as a dynamic link library (DLL): Add unit tests in the same project as the product code.

Go to the procedure To add unit tests in the same project.

Create the tests

  • If your tests must use members that aren't exported by the DLL project, and the project under test is built as a dynamic library, consider converting it to a static library.

    1. In Solution Explorer, on the shortcut menu of the project under test, choose Properties. The project Properties window opens.

    2. Choose Configuration Properties > General.

    3. Set Configuration Type to Static Library (.lib).

    Continue with the procedure To link the tests to the object or library files.

To reference exported DLL functions from the test project

  • If the DLL project exports the functions that you want to test, then you can add a reference to the code project from the test project.

    1. Create a Native Unit Test Project.

      1. On the File menu, choose New > Project. In the Add a New Project dialog, set Language to C++ and type "test" into the search box. Then choose the Native Unit Test Project.

    2. In Solution Explorer, right-click on the test project, then choose Add > Reference.

    3. Select Projects, and then the project to be tested.

      Choose the Add button.

    4. In the properties for the test project, add the location of the project under test to the Include Directories.

      Choose Configuration Properties > VC++ Directories > Include Directories.

      Choose Edit, and then add the header directory of the project under test.

    Go to Write the unit tests.

To link the tests to the object or library files

  • If the DLL doesn't export the functions that you want to test, you can add the output .obj or .lib file to the dependencies of the test project.

    1. Create a Native Unit Test Project.

      1. On the File menu, choose New > Project. In the Add a New Project dialog, set Language to C++ and type "test" into the search box. Then choose the Native Unit Test Project.

    2. In Solution Explorer, on the shortcut menu of the test project, choose Properties.

    3. Choose Configuration Properties > Linker > Input > Additional Dependencies.

      Choose Edit, and add the names of the .obj or .lib files. Don't use the full path names.

    4. Choose Configuration Properties > Linker > General > Additional Library Directories.

      Choose Edit, and add the directory path of the .obj or .lib files. The path is typically within the build folder of the project under test.

    5. Choose Configuration Properties > VC++ Directories > Include Directories.

      Choose Edit, and then add the header directory of the project under test.

    Go to Write the unit tests.

To add unit tests in the same project

  1. Modify the product code project properties to include the headers and library files that are required for unit testing.

    1. In Solution Explorer, in the shortcut menu of the project under test, choose Properties. The project Properties window opens.

    2. Choose Configuration Properties > VC++ Directories.

    3. Edit the Include and Library directories:

      Directory Property
      Include Directories $(VCInstallDir)Auxiliary\VS\UnitTest\include
      Library Directories $(VCInstallDir)Auxiliary\VS\UnitTest\lib

  2. Add a C++ Unit Test file:

    1. Right-click on the project node in Solution Explorer and choose Add > New Item.

    2. In the Add New Item dialog, select C++ File (.cpp), give it an appropriate name, and then choose Add.

    Go to Write the unit tests.

Write the unit tests

  1. In each unit test code file, add an #include statement for the headers of the project under test.

  2. Add test classes and methods to the unit test code files. For example:

    #include "stdafx.h"
#include "CppUnitTest.h"
#include "MyProjectUnderTest.h"
using namespace Microsoft::VisualStudio::CppUnitTestFramework;
namespace MyTest
{
  TEST_CLASS(MyTests)
  {
  public:
      TEST_METHOD(MyTestMethod)
      {
          Assert::AreEqual(MyProject::Multiply(2,3), 6);
      }
  };
}

Run the tests

  1. On the Test menu, choose Windows > Test Explorer.

  2. If not all of your tests are visible in the window, build the test project: right-click its node in Solution Explorer and choose Build or Rebuild.

  3. In Test Explorer, choose Run All, or select the specific tests you want to run. Right-click on a test for other options, for example, to run it in debug mode with breakpoints enabled.

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