Document makefile options

See #653

Makefile

@@ -1,16 +1,31 @@
 # See the documentation on how to run the tests.
 
+# Which DAV server to run the tests against (radicale, xandikos, skip, owncloud, nextcloud, ...)
 export DAV_SERVER := skip
+
+# release (install release versions of dependencies)
+# development (install development versions of some of vdirsyncer's dependencies)
+# or minimal (install oldest version of each dependency that is supported by vdirsyncer)
 export REQUIREMENTS := release
-export TESTSERVER_BASE := ./tests/storage/servers/
-export CI := false
-export COVERAGE := $(CI)
+
+# Set this to true if you run vdirsyncer's test as part of e.g. packaging.
 export DETERMINISTIC_TESTS := false
+
+# Run the etesync testsuite.
 export ETESYNC_TESTS := false
 
-CODECOV_PATH = /tmp/codecov.sh
+# Assume to run in Travis. Don't use this outside of a virtual machine. It will
+# heavily "pollute" your system.
+export CI := false
 
+# Whether to generate coverage data while running tests.
+export COVERAGE := $(CI)
+
+# Additional arguments that should be passed to py.test.
 PYTEST_ARGS =
+
+# Variables below this line are not very interesting for getting started.
+
 TEST_EXTRA_PACKAGES =
 ifeq ($(COVERAGE), true)
 	TEST_EXTRA_PACKAGES += pytest-cov
@@ -22,6 +37,9 @@ ifeq ($(ETESYNC_TESTS), true)
 	TEST_EXTRA_PACKAGES += django djangorestframework wsgi_intercept drf-nested-routers
 endif
 
+export TESTSERVER_BASE := ./tests/storage/servers/
+CODECOV_PATH = /tmp/codecov.sh
+
 ifeq ($(CI), true)
 test:
 	curl -s https://codecov.io/bash > $(CODECOV_PATH)

docs/contributing.rst

@@ -93,6 +93,10 @@ Then you can run::
     make style  # Stylechecker
     make docs  # Build the HTML docs, output is at docs/_build/html/
 
+The ``Makefile`` has a lot of options that allow you to control which tests are
+run, and which servers are tested. Take a look at its code where they are all
+initialized and documented.
+
 If you have any questions, feel free to open issues about it.
 
 Structure of the testsuite