def _trialSortAlgorithm(self, sorter):
        """
        Right now, halfway by accident, trial sorts like this:

            1. all modules are grouped together in one list and sorted.

            2. within each module, the classes are grouped together in one list
               and sorted.

            3. finally within each class, each test method is grouped together
               in a list and sorted.

        This attempts to return a sorted list of testable thingies following
        those rules, so that we can compare the behavior of loadPackage.

        The things that show as 'cases' are errors from modules which failed to
        import, and test methods.  Let's gather all those together.
        """
        pkg = getModule('uberpackage')
        testModules = []
        for testModule in pkg.walkModules():
            if testModule.name.split(".")[-1].startswith("test_"):
                testModules.append(testModule)
        sortedModules = sorted(testModules, key=sorter) # ONE
        for modinfo in sortedModules:
            # Now let's find all the classes.
            module = modinfo.load(None)
            if module is None:
                yield modinfo
            else:
                testClasses = []
                for attrib in modinfo.iterAttributes():
                    if runner.isTestCase(attrib.load()):
                        testClasses.append(attrib)
                sortedClasses = sorted(testClasses, key=sorter) # TWO
                for clsinfo in sortedClasses:
                    testMethods = []
                    for attr in clsinfo.iterAttributes():
                        if attr.name.split(".")[-1].startswith('test'):
                            testMethods.append(attr)
                    sortedMethods = sorted(testMethods, key=sorter) # THREE
                    for methinfo in sortedMethods:
                        yield methinfo

        Right now, halfway by accident, trial sorts like this:

            1. all modules are grouped together in one list and sorted.

            2. within each module, the classes are grouped together in one list
               and sorted.

            3. finally within each class, each test method is grouped together
               in a list and sorted.

        This attempts to return a sorted list of testable thingies following
        those rules, so that we can compare the behavior of loadPackage.

        The things that show as 'cases' are errors from modules which failed to
        import, and test methods.  Let's gather all those together.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/trial/test/test_loader.py