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| -rw-r--r-- | doc/subprocess.rst | 16 |
1 files changed, 13 insertions, 3 deletions
diff --git a/doc/subprocess.rst b/doc/subprocess.rst index 9e223d8e..15fa4c22 100644 --- a/doc/subprocess.rst +++ b/doc/subprocess.rst @@ -26,9 +26,19 @@ multiple coverage.py runs will each write their data to a distinct file. Configuring Python for subprocess coverage ------------------------------------------ -To measure coverage in subprocesses, you have to do two things: set a value for -the ``COVERAGE_PROCESS_START`` environment variable, and then invoke -:func:`coverage.process_startup`. +Measuring coverage in subprocesses is a little tricky. When you spawn a +subprocess, you are invoking Python to run your program. Usually, to get +coverage measurement, you have to use coverage.py to run your program. +Your subprocess won't be using coverage.py, so we have to convince Python +to use coverage even when not explicitly invokved. + +To do that, we'll configure Python to run a little coverage.py code when it +starts. That code will look for an environment variable that tells it to +start coverage measurement at the start of the process. + +To arrange all this, you have to do two things: set a value for the +``COVERAGE_PROCESS_START`` environment variable, and then configure Python to +invoke :func:`coverage.process_startup` when Python processes start. How you set ``COVERAGE_PROCESS_START`` depends on the details of how you create subprocesses. As long as the environment variable is visible in your subprocess, |