Make --subunit --list-tests only print test IDs

This is not really correct, but it simplifies Launchpad's testrepository
plumbing for now.

Based on work by Benji York in Launchpad's zope.testing fork.

src/zope/testrunner/formatter.py

@@ -1055,12 +1055,8 @@ def _emit_exists(self, test):
 
     def list_of_tests(self, tests, layer_name):
         """Report a list of test names."""
-        self._enter_layer(layer_name)
         for test in tests:
-            self._subunit.startTest(test)
-            self._emit_exists(test)
-            self._subunit.stopTest(test)
-        self._exit_layer(layer_name)
+            print(test.id())
 
     def garbage(self, garbage):
         """Report garbage generated by tests."""
@@ -1312,6 +1308,17 @@ def _subunit_factory(cls, stream):
         result.startTestRun()
         return result
 
+    # Undo Launchpad's subunit v1 hack to print test IDs directly rather
+    # than using a subunit stream; we only use that in v1 mode.
+    def list_of_tests(self, tests, layer_name):
+        """Report a list of test names."""
+        self._enter_layer(layer_name)
+        for test in tests:
+            self._subunit.startTest(test)
+            self._emit_exists(test)
+            self._subunit.stopTest(test)
+        self._exit_layer(layer_name)
+
     def error(self, message):
         """Report an error."""
         # XXX: Mostly used for user errors, sometimes used for errors in the

src/zope/testrunner/tests/testrunner-subunit.rst

@@ -107,32 +107,19 @@ Once the layer is set up, all future tests are tagged with
 Listing tests
 -------------
 
-A subunit stream is a stream of test results, more or less, so the most
-natural way of listing tests in subunit is to simply emit successful test
-results without actually running the tests.
-
-Note that in this stream, we don't emit fake tests for the layer set up and
-tear down, because it simply doesn't happen.
-
-We also don't include the dependent layers in the stream (in this case Layer1
-and Layer12), since they are not provided to the reporter.
+This version of zope.testrunner is customized to list tests by just printing
+all their IDs to stdout even in subunit mode.  This is not really correct
+and should be fixed at some point, but it simplifies Launchpad's
+testrepository plumbing.
 
     >>> sys.argv = 'test --layer 122 --list-tests -t TestNotMuch'.split()
     >>> testrunner.run_internal(defaults)
-    tags: zope:layer:samplelayers.Layer122
-    test: sample1.sampletests.test122.TestNotMuch.test_1
-    successful: sample1.sampletests.test122.TestNotMuch.test_1
-    test: sample1.sampletests.test122.TestNotMuch.test_2
-    successful: sample1.sampletests.test122.TestNotMuch.test_2
-    test: sample1.sampletests.test122.TestNotMuch.test_3
-    successful: sample1.sampletests.test122.TestNotMuch.test_3
-    test: sampletests.test122.TestNotMuch.test_1
-    successful: sampletests.test122.TestNotMuch.test_1
-    test: sampletests.test122.TestNotMuch.test_2
-    successful: sampletests.test122.TestNotMuch.test_2
-    test: sampletests.test122.TestNotMuch.test_3
-    successful: sampletests.test122.TestNotMuch.test_3
-    tags: -zope:layer:samplelayers.Layer122
+    sample1.sampletests.test122.TestNotMuch.test_1
+    sample1.sampletests.test122.TestNotMuch.test_2
+    sample1.sampletests.test122.TestNotMuch.test_3
+    sampletests.test122.TestNotMuch.test_1
+    sampletests.test122.TestNotMuch.test_2
+    sampletests.test122.TestNotMuch.test_3
     False