Allow tracing of TestResource activity by passing a trace_function to TestResource, fixing bug 284125.

3 files changed, 26 insertions, 3 deletions

diff --git a/NEWS b/NEWS
index 004e376..260b7d9 100644
--- a/NEWS
+++ b/NEWS
@@ -21,6 +21,10 @@ IN DEVELOPMENT
 
     * Started keeping a NEWS file! (Jonathan Lange)
 
+    * A trace_function can be supplied when constructing TestResource objects,
+      to allow debugging of when resources are made/cleaned. (Robert Collins,
+      #284125)
+
   BUG FIXES:
 
     * Calling getResource on a dirty resource now triggers a clean and re-make
diff --git a/lib/testresources/__init__.py b/lib/testresources/__init__.py
index 4bc7ef4..adccecd 100644
--- a/lib/testresources/__init__.py
+++ b/lib/testresources/__init__.py
@@ -197,14 +197,22 @@ class TestResource(object):
     setUpCost = 1
     tearDownCost = 1
 
-    def __init__(self):
+    def __init__(self, trace_function=None):
+        """Create a TestResource object.
+
+        :param trace_function: A callable that takes strings to output. This
+            will be called with trace messages when the resource is made and
+            cleaned.
+        """
         self._dirty = False
         self._uses = 0
         self._currentResource = None
         self.resources = list(getattr(self.__class__, "resources", []))
+        self._trace = trace_function or (lambda x:"")
 
     def _clean_all(self, resource):
         """Clean the dependencies from resource, and then resource itself."""
+        self._trace("clean: %s\n" % self)
         self.clean(resource)
         for name, manager in self.resources:
             manager.finishedWith(getattr(resource, name))
@@ -271,6 +279,7 @@ class TestResource(object):
 
     def _make_all(self):
         """Make the dependencies of this resource and this resource."""
+        self._trace("make: %s\n" % self)
         dependency_resources = {}
         for name, resource in self.resources:
             dependency_resources[name] = resource.getResource()
diff --git a/lib/testresources/tests/test_test_resource.py b/lib/testresources/tests/test_test_resource.py
index a11c987..83abfbe 100644
--- a/lib/testresources/tests/test_test_resource.py
+++ b/lib/testresources/tests/test_test_resource.py
@@ -44,8 +44,8 @@ class MockResourceInstance(object):
 class MockResource(testresources.TestResource):
     """Mock resource that logs the number of make and clean calls."""
 
-    def __init__(self):
-        testresources.TestResource.__init__(self)
+    def __init__(self, trace_function=None):
+        testresources.TestResource.__init__(self, trace_function=trace_function)
         self.makes = 0
         self.cleans = 0
 
@@ -275,3 +275,13 @@ class TestTestResource(testtools.TestCase):
         self.assertEqual(1, resource_manager.makes)
         resource = resource_manager.getResource()
         self.assertEqual(2, resource_manager.makes)
+
+    def testTraceFunction(self):
+        output = []
+        resource_manager = MockResource(trace_function=output.append)
+        expected = ["make: %s\n" % resource_manager]
+        r = resource_manager.getResource()
+        self.assertEqual(expected, output)
+        expected.append("clean: %s\n" % resource_manager)
+        resource_manager.finishedWith(r)
+        self.assertEqual(expected, output)