New method Engine.find_task_by_id() to retrieve a task object given…

… its persistent ID.

gc3libs/tests/test_engine.py

@@ -447,6 +447,57 @@ def test_engine_cannot_find_task_by_id_if_no_store():
             with pytest.raises(KeyError):
                 engine.find_task_by_id(task_id)
 
+def test_engine_find_task_by_id():
+    """
+    Test that saved tasks are can be retrieved from the Engine given their ID only.
+    """
+    with temporary_core() as core:
+        with temporary_directory() as tmpdir:
+            store = FilesystemStore(tmpdir)
+            engine = Engine(core, store=store)
+
+            task = SuccessfulApp()
+            store.save(task)
+            engine.add(task)
+
+            task_id = task.persistent_id
+            assert_equal(task, engine.find_task_by_id(task_id))
+
+
+@raises(KeyError)
+def test_engine_cannot_find_task_by_id_if_not_saved():
+    """
+    Test that *unsaved* tasks are cannot be retrieved from the Engine given their ID only.
+    """
+    with temporary_core() as core:
+        with temporary_directory() as tmpdir:
+            store = FilesystemStore(tmpdir)
+            engine = Engine(core, store=store)
+
+            task = SuccessfulApp()
+            engine.add(task)
+
+            store.save(task)  # guarantee it has a `.persistent_id`
+            task_id = task.persistent_id
+            engine.find_task_by_id(task_id)
+
+
+@raises(KeyError)
+def test_engine_cannot_find_task_by_id_if_no_store():
+    """
+    Test that `Engine.find_task_by_id` always raises `KeyError` if the Engine has no associated store.
+    """
+    with temporary_engine() as engine:
+       with temporary_directory() as tmpdir:
+            store = FilesystemStore(tmpdir)
+
+            task = SuccessfulApp()
+            engine.add(task)
+
+            store.save(task)  # guarantee it has a `.persistent_id`
+            task_id = task.persistent_id
+            engine.find_task_by_id(task_id)
+
 
 if __name__ == "__main__":
     import pytest