Add import-fails code as a fixture

tests/conftest.py

@@ -1054,3 +1054,24 @@ def rpc_balance():
 def testdatadir() -> Path:
     """Return the path where testdata files are stored"""
     return (Path(__file__).parent / "testdata").resolve()
+
+
+@pytest.fixture(scope="function")
+def import_fails() -> None:
+    # Source of this test-method:
+    # https://stackoverflow.com/questions/2481511/mocking-importerror-in-python
+    import builtins
+    realimport = builtins.__import__
+
+    def mockedimport(name, *args, **kwargs):
+        if name in ["filelock"]:
+            raise ImportError(f"No module named '{name}'")
+        return realimport(name, *args, **kwargs)
+
+    builtins.__import__ = mockedimport
+
+    # Run test - then cleanup
+    yield
+
+    # restore previous importfunction
+    builtins.__import__ = realimport

tests/optimize/test_hyperopt.py

@@ -190,19 +190,9 @@ def test_hyperoptlossresolver_wrongname(mocker, default_conf, caplog) -> None:
         HyperOptLossResolver(default_conf, ).hyperopt
 
 
-def test_start_not_installed(mocker, default_conf, caplog) -> None:
+def test_start_not_installed(mocker, default_conf, caplog, import_fails) -> None:
     start_mock = MagicMock()
     patched_configuration_load_config_file(mocker, default_conf)
-    # Source of this test-method: https://stackoverflow.com/questions/2481511/mocking-importerror-in-python
-    import builtins
-    realimport = builtins.__import__
-
-    def mockedimport(name, *args, **kwargs):
-        if name == "filelock":
-            raise ImportError("No module named 'filelock'")
-        return realimport(name, *args, **kwargs)
-
-    builtins.__import__ = mockedimport
 
     mocker.patch('freqtrade.optimize.hyperopt.Hyperopt.start', start_mock)
     patch_exchange(mocker)
@@ -217,9 +207,6 @@ def test_start_not_installed(mocker, default_conf, caplog) -> None:
     with pytest.raises(OperationalException, match=r"Please ensure that the hyperopt dependencies"):
         start_hyperopt(args)
 
-    # restore previous importfunction
-    builtins.__import__ = realimport
-
 
 def test_start(mocker, default_conf, caplog) -> None:
     start_mock = MagicMock()