Enforcing or Handling Missing Tests with CTEST_NO_TESTS_ACTION in CMake

CTEST_NO_TESTS_ACTION

• Values
  It can take one of the following values:
  • error: If set to error, ctest will terminate with an error code, indicating that the absence of tests is considered a problem. This is useful for ensuring that your project always includes a test suite.
  • ignore: With this value, ctest will simply continue execution without running any tests. This might be suitable if you're building a project that doesn't necessarily require testing or if the tests are built conditionally.
  • empty: Similar to ignore, but ctest will explicitly display a message stating that no tests were found. This can be helpful for informative purposes.
  • Unset (default)
    If CTEST_NO_TESTS_ACTION is not explicitly set, the default behavior of ctest is typically to display a warning message indicating that no tests were found.
• Purpose
  This environment variable in CMake controls how the ctest tool, which is responsible for running tests within your project, behaves when it encounters a situation where there are no tests to execute.

Environment Variables

• Setting CTEST_NO_TESTS_ACTION
  You can set this environment variable in various ways, depending on your environment:
  • Command Line
    Set it before invoking ctest using your shell's syntax (e.g., export CTEST_NO_TESTS_ACTION=error in Bash).
  • CMakeLists.txt
    While not directly supported within CMakeLists.txt, you can use environment variables set externally.
• Definition
  Environment variables are essentially named settings that can influence the behavior of programs or processes. They provide a way to store and access configuration values outside of the code itself.

Value	Behavior
error	ctest exits with an error code
ignore	ctest continues without running tests
empty	ctest displays a message and continues
Unset (default)	ctest usually displays a warning message

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Setting CTEST_NO_TESTS_ACTION from the Command Line (Enforcing Tests)

# Assuming you have tests in your project

# Enforce test presence by exiting with error if no tests are found
export CTEST_NO_TESTS_ACTION=error
ctest

# Alternatively, display an informative message
export CTEST_NO_TESTS_ACTION=empty
ctest

Conditional Compilation Based on Environment Variables (Example in CMakeLists.txt)

# Assuming an environment variable `BUILD_TESTS` is set

if(DEFINED ENV{BUILD_TESTS})
  # Build tests if BUILD_TESTS is set (value doesn't matter)
  enable_testing()
  add_executable(my_test my_test.cpp)
  target_link_libraries(my_test my_library)
  add_test(NAME my_test_exec COMMAND ctest -N -E my_test)
else()
  # Inform the user that tests are not built
  message(STATUS "Skipping test build as BUILD_TESTS is not set.")
endif()

In this example, the presence of the environment variable BUILD_TESTS determines whether tests are built and run. This provides flexibility in your build process, allowing you to control test execution based on external factors.

Advanced: Using CMake Toolchain (Optional)

If you have a complex build environment, you might consider using a CMake toolchain file. This file can define environment variables that are then used during the build process. However, this is an advanced technique and may not be necessary for simpler projects.

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1. • Write a script (e.g., Bash, Python) that checks for the existence of tests before running ctest.
   • The script can leverage tools like ctest --list-tests to verify test presence.
   • Based on the results, the script can decide whether to proceed with ctest or raise an error/informative message.
   • Integrate this script into your build process using CMake's execute_process command.

2. Custom CMake Target
   

   • Create a custom CMake target that depends on your test executables.
   • Use the TARGET_LINK_LIBRARIES or ADD_DEPENDENCIES commands to establish this dependency.
   • If no test executables exist, CMake will fail to build this target, indicating a missing test suite.

3. Leverage Build System Features
   

   • Some build systems like Make, Ninja, or custom build systems might offer mechanisms to enforce test presence.
   • Explore these build system features to achieve the desired behavior.

4. Continuous Integration (CI) Integration
   

   • If you're using CI tools, configure them to check for the existence of test files or targets before triggering test execution.
   • This allows you to enforce testing within your CI pipeline.