# CTEST_PARALLEL_LEVEL

This is a CMake Environment Variable. Its initial value is taken from the calling process environment.

Specify the number of tests for CTest to run in parallel. For example, if `CTEST_PARALLEL_LEVEL` is set to 8, CTest will run up to 8 tests concurrently as if `ctest` were invoked with the `--parallel 8` option.

Changed in version 3.29: The value may be empty, or `0`, to let ctest use a default level of parallelism, or unbounded parallelism, respectively, as documented by the `ctest --parallel` option.

On Windows, environment variables cannot be set to an empty string. CTest will interpret a whitespace-only string as empty.

In CMake 3.28 and earlier, an empty or `0` value was equivalent to `1`.

See `ctest(1)` for more information on parallel test execution.