First cut of testing infrastructure for recipes.

third_party/coverage-3.6/doc/subprocess.rst

+.. _subprocess:
+
+======================
+Measuring subprocesses
+======================
+
+:history: 20100224T201800, new for 3.3.
+:history: 20100725T211700, updated for 3.4.
+
+
+Complex test suites may spawn subprocesses to run tests, either to run them in
+parallel, or because subprocess behavior is an important part of the system
+under test. Measuring coverage in those subprocesses can be tricky because you
+have to modify the code spawning the process to invoke coverage.py.
+
+There's an easier way to do it: coverage.py includes a function,
+:func:`coverage.process_startup` designed to be invoked when Python starts.  It
+examines the ``COVERAGE_PROCESS_START`` environment variable, and if it is set,
+begins coverage measurement. The environment variable's value will be used as
+the name of the :ref:`configuration file <config>` to use.
+
+When using this technique, be sure to set the parallel option to true so that
+multiple coverage.py runs will each write their data to a distinct file.
+
+
+Configuring Python for subprocess coverage
+------------------------------------------
+
+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,
+it will work.
+
+You can configure your Python installation to invoke the ``process_startup``
+function in two ways:
+
+#. Create or append to sitecustomize.py to add these lines::
+
+    import coverage
+    coverage.process_startup()
+
+#. Create a .pth file in your Python installation containing::
+
+    import coverage; coverage.process_startup()
+
+The sitecustomize.py technique is cleaner, but may involve modifying an existing
+sitecustomize.py, since there can be only one.  If there is no sitecustomize.py
+already, you can create it in any directory on the Python path.
+
+The .pth technique seems like a hack, but works, and is documented behavior.
+On the plus side, you can create the file with any name you like so you don't
+have to coordinate with other .pth files.  On the minus side, you have to create
+the file in a system-defined directory, so you may need privileges to write it.