It’s often useful to set per-test environment variables in CMake’s CTest testing frontend. The environment variables appear and disappear with the start and end of each test, in isolation from any other tests that may be running in parallel. This is accomplished via CMake test properties ENVIRONMENT and ENVIRONMENT_MODIFICATION.

Example: set environment variable FOO=1 for a test “bar” like:

set_property(TEST bar PROPERTY ENVIRONMENT "FOO=1")

multiple variables are set with a CMake list (semicolon delimited) like:

set_property(TEST bar PROPERTY ENVIRONMENT "FOO=1;BAZ=0")

Here comes an issue. In general, Windows needs DLLs to be on the current working directory or in environment variable PATH. We handle this by a script that appends to PATH for CTest on Windows:

In Python likewise set/unset environment variables within tests using PyTest monkeypatch fixture.