2 files changed, 67 insertions, 2 deletions
diff --git a/lib/testresources/__init__.py b/lib/testresources/__init__.py
index 820d62b..e8c0685 100644
--- a/lib/testresources/__init__.py
+++ b/lib/testresources/__init__.py
@@ -246,11 +246,29 @@ class TestResource(object):
         """
         if self._uses == 0:
             self._setResource(self.make_all())
-        elif self._dirty:
+        elif self.isDirty():
             self._resetResource(self._currentResource)
         self._uses += 1
         return self._currentResource
 
+    def isDirty(self):
+        """Return True if this managers cached resource is dirty.
+        
+        Calling when the resource is not currently held has undefined
+        behaviour.
+        """
+        if self._dirty:
+            return True
+        for name, mgr in self.resources:
+            if mgr.isDirty():
+                return True
+            res = mgr.getResource()
+            try:
+                if res is not getattr(self._currentResource, name):
+                    return True
+            finally:
+                mgr.finishedWith(res)
+
     def make_all(self):
         """Make the dependencies of this resource and this resource."""
         dependency_resources = {}
diff --git a/lib/testresources/tests/test_test_resource.py b/lib/testresources/tests/test_test_resource.py
index 9c33d86..a11c987 100644
--- a/lib/testresources/tests/test_test_resource.py
+++ b/lib/testresources/tests/test_test_resource.py
@@ -29,6 +29,18 @@ def test_suite():
     return result
 
 
+class MockResourceInstance(object):
+
+    def __init__(self, name):
+        self._name = name
+
+    def __cmp__(self, other):
+        return cmp(self.__dict__, other.__dict__)
+
+    def __repr__(self):
+        return self._name
+
+
 class MockResource(testresources.TestResource):
     """Mock resource that logs the number of make and clean calls."""
 
@@ -42,7 +54,7 @@ class MockResource(testresources.TestResource):
 
     def make(self, dependency_resources):
         self.makes += 1
-        return "Boo!"
+        return MockResourceInstance("Boo!")
 
 
 class TestTestResource(testtools.TestCase):
@@ -130,6 +142,41 @@ class TestTestResource(testtools.TestCase):
         resource_manager.getResource()
         self.assertEqual(1, resource_manager.makes)
 
+    def testIsDirty(self):
+        resource_manager = MockResource()
+        r = resource_manager.getResource()
+        resource_manager.dirtied(r)
+        self.assertTrue(resource_manager.isDirty())
+        resource_manager.finishedWith(r)
+
+    def testIsDirtyIsTrueIfDependenciesChanged(self):
+        resource_manager = MockResource()
+        dep1 = MockResource()
+        dep2 = MockResource()
+        dep3 = MockResource()
+        resource_manager.resources.append(("dep1", dep1))
+        resource_manager.resources.append(("dep2", dep2))
+        resource_manager.resources.append(("dep3", dep3))
+        r = resource_manager.getResource()
+        dep2.dirtied(r.dep2)
+        r2 =dep2.getResource()
+        self.assertTrue(resource_manager.isDirty())
+        resource_manager.finishedWith(r)
+        dep2.finishedWith(r2)
+
+    def testIsDirtyIsTrueIfDependenciesAreDirty(self):
+        resource_manager = MockResource()
+        dep1 = MockResource()
+        dep2 = MockResource()
+        dep3 = MockResource()
+        resource_manager.resources.append(("dep1", dep1))
+        resource_manager.resources.append(("dep2", dep2))
+        resource_manager.resources.append(("dep3", dep3))
+        r = resource_manager.getResource()
+        dep2.dirtied(r.dep2)
+        self.assertTrue(resource_manager.isDirty())
+        resource_manager.finishedWith(r)
+
     def testRepeatedGetResourceCallsMakeResourceOnceOnly(self):
         resource_manager = MockResource()
         resource_manager.getResource()