Merge support for trace_functions in TestResource.

3 files changed, 32 insertions, 3 deletions

diff --git a/NEWS b/NEWS
index e78c696..ffaf75f 100644
--- a/NEWS
+++ b/NEWS
@@ -26,6 +26,10 @@ 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 da26136..2c1b086 100644
--- a/lib/testresources/__init__.py
+++ b/lib/testresources/__init__.py
@@ -197,17 +197,26 @@ 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 (event_label,
+            "start"|"stop", resource). This will be called with to tracec
+            events 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,y,z:"")
 
     def _clean_all(self, resource):
         """Clean the dependencies from resource, and then resource itself."""
+        self._trace("clean", "start", self)
         self.clean(resource)
         for name, manager in self.resources:
             manager.finishedWith(getattr(resource, name))
+        self._trace("clean", "stop", self)
 
     def clean(self, resource):
         """Override this to class method to hook into resource removal."""
@@ -271,12 +280,14 @@ class TestResource(object):
 
     def _make_all(self):
         """Make the dependencies of this resource and this resource."""
+        self._trace("make", "start", self)
         dependency_resources = {}
         for name, resource in self.resources:
             dependency_resources[name] = resource.getResource()
         result = self.make(dependency_resources)
         for name, value in dependency_resources.items():
             setattr(result, name, value)
+        self._trace("make", "stop", self)
         return result
 
     def make(self, dependency_resources):
diff --git a/lib/testresources/tests/test_test_resource.py b/lib/testresources/tests/test_test_resource.py
index 4d89469..9a3bedd 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
 
@@ -325,3 +325,17 @@ class TestTestResource(testtools.TestCase):
         self.assertEqual(1, resource_manager.makes)
         resource = resource_manager.getResource()
         self.assertEqual(2, resource_manager.makes)
+
+    def testTraceFunction(self):
+        output = []
+        def trace(operation, phase, mgr):
+            output.append((operation, phase, mgr))
+        resource_manager = MockResource(trace_function=trace)
+        expected = [("make", "start", resource_manager),
+            ("make", "stop", resource_manager)]
+        r = resource_manager.getResource()
+        self.assertEqual(expected, output)
+        expected.extend([("clean", "start", resource_manager),
+            ("clean", "stop", resource_manager)])
+        resource_manager.finishedWith(r)
+        self.assertEqual(expected, output)