Method for reloading a topology (not bind to an api handler)

Ref https://github.com/GNS3/gns3-gui/issues/1243

tests/controller/test_topology.py

@@ -15,12 +15,15 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+import json
+import pytest
+import aiohttp
 from unittest.mock import MagicMock
 from tests.utils import asyncio_patch
 
 from gns3server.controller.project import Project
 from gns3server.controller.compute import Compute
-from gns3server.controller.topology import project_to_topology
+from gns3server.controller.topology import project_to_topology, load_topology
 from gns3server.version import __version__
 
 
@@ -60,3 +63,45 @@ def test_basic_topology(tmpdir, async_run, controller):
     assert topo["topology"]["links"][0] == link.__json__()
     assert topo["topology"]["computes"][0] == compute.__json__()
 
+
+
+def test_load_topology(tmpdir):
+    data = {
+        "project_id": "69f26504-7aa3-48aa-9f29-798d44841211",
+        "name": "Test",
+        "revision": 5,
+        "topology": {
+            "nodes": [],
+            "links": [],
+            "computes": []
+        },
+        "type": "topology",
+        "version": __version__}
+
+    path = str(tmpdir / "test.gns3")
+    with open(path, "w+") as f:
+        json.dump(data, f)
+    topo = load_topology(path)
+    assert topo == data
+
+def test_load_topology_file_error(tmpdir):
+    path = str(tmpdir / "test.gns3")
+    with pytest.raises(aiohttp.web.HTTPConflict):
+        topo = load_topology(path)
+
+
+def test_load_old_topology(tmpdir):
+    data = {
+        "project_id": "69f26504-7aa3-48aa-9f29-798d44841211",
+        "name": "Test",
+        "revision": 4,
+        "topology": {
+        },
+        "type": "topology",
+        "version": __version__}
+
+    path = str(tmpdir / "test.gns3")
+    with open(path, "w+") as f:
+        json.dump(data, f)
+    with pytest.raises(aiohttp.web.HTTPConflict):
+        topo = load_topology(path)