Add bt-error to UI backtest method.

freqtrade/rpc/api_server/api_backtest.py

@@ -29,6 +29,7 @@ router = APIRouter()
 async def api_start_backtest(  # noqa: C901
         bt_settings: BacktestRequest, background_tasks: BackgroundTasks,
         config=Depends(get_config), ws_mode=Depends(is_webserver_mode)):
+    ApiServer._bt['bt_error'] = None
     """Start backtesting if not done so already"""
     if ApiServer._bgtask_running:
         raise RPCException('Bot Background task already running')
@@ -120,6 +121,7 @@ async def api_start_backtest(  # noqa: C901
 
         except (Exception, OperationalException, DependencyException) as e:
             logger.exception(f"Backtesting caused an error: {e}")
+            ApiServer._bt['bt_error'] = str(e)
             pass
         finally:
             ApiServer._bgtask_running = False
@@ -162,6 +164,14 @@ def api_get_backtest(ws_mode=Depends(is_webserver_mode)):
             "progress": 0,
             "status_msg": "Backtest not yet executed"
         }
+    if ApiServer._bt['bt_error']:
+        return {
+            "status": "error",
+            "running": False,
+            "step": "",
+            "progress": 0,
+            "status_msg": f"Backtest failed with {ApiServer._bt['bt_error']}"
+        }
 
     return {
         "status": "ended",

freqtrade/rpc/api_server/webserver.py

@@ -41,6 +41,7 @@ class ApiServer(RPCHandler):
         'data': None,
         'timerange': None,
         'last_config': {},
+        'bt_error': None,
     }
     _has_rpc: bool = False
     _bgtask_running: bool = False

tests/rpc/test_rpc_apiserver.py

@@ -1737,9 +1737,15 @@ def test_api_backtesting(botclient, mocker, fee, caplog, tmpdir):
     data['stake_amount'] = 101
 
     mocker.patch('freqtrade.optimize.backtesting.Backtesting.backtest_one_strategy',
-                 side_effect=DependencyException())
+                 side_effect=DependencyException('DeadBeef'))
     rc = client_post(client, f"{BASE_URI}/backtest", data=data)
-    assert log_has("Backtesting caused an error: ", caplog)
+    assert log_has("Backtesting caused an error: DeadBeef", caplog)
+
+    rc = client_get(client, f"{BASE_URI}/backtest")
+    assert_response(rc)
+    result = rc.json()
+    assert result['status'] == 'error'
+    assert 'Backtest failed' in result['status_msg']
 
     # Delete backtesting to avoid leakage since the backtest-object may stick around.
     rc = client_delete(client, f"{BASE_URI}/backtest")