Allow us to run tests from external XBlock repositories

openedx/tests/xblock_integration/test_external_xblocks.py

+"""
+This will run tests on all XBlocks in the `xblock.test.v0`
+entrypoint. Did you notice something about that entry point? It ends
+with a v0. That means this is not finished. At some point, we might
+stop running v0 tests, replacing them with test case failures, and
+run v1 tests only.
+
+That be the dragon here.
+"""
+import pkg_resources
+
+
+class DuplicateXBlockTest(Exception):
+    '''
+    This exception is shown if there are multiple entry points with the same
+    class name for a test. In most cases, this means you have two versions
+    of the same XBlock installed, or two XBlocks with namespace collisions. In
+    either case, it'd be nice to resolve (likely by renaming tests as they
+    come in, hopefully still being careful to catch collisions which might
+    effect deployed XBlocks. See discussion at:
+      https://github.com/edx/edx-platform/pull/11032#discussion_r48097392).
+    '''
+    pass
+
+
+class InvalidTestName(Exception):
+    '''
+    This means you have an entry point for a test that does not correspond
+    to a properly named test class. For example, if you cut-and-paste entry
+    points in `setup.py`, and forgot to repoint the class (so it points to
+    `DoneXBlock` instead of `TestDone`), or otherwise made an error, you
+    will see this exception.
+    '''
+    pass
+
+xblock_loaded = False  # pylint: disable=invalid-name
+
+for entrypoint in pkg_resources.iter_entry_points(group="xblock.test.v0"):  # pylint: disable=no-member
+    plugin = entrypoint.load()
+    classname = plugin.__name__
+    if classname in globals():
+        raise DuplicateXBlockTest(classname)
+    if not classname.startswith("Test"):
+        raise InvalidTestName("Test class should start with 'Test': " + classname)
+    # This should never happen, but while we're testing for class name
+    # validity, we figured it was okay to be a little overly defensive.
+    # See discussion at:
+    # https://github.com/edx/edx-platform/pull/11032#discussion_r48097392
+    if not classname.replace("_", "").isalnum():
+        raise InvalidTestName("Python variables should be letters, numbers, and underscores: " + classname)
+    globals()[classname] = plugin
+    print "Loading XBlock test: " + classname
+    xblock_loaded = True