Ensure testing framework is loaded only if dependencies are installed (…

…#624)

webviz_config/testing/__init__.py

@@ -1 +1,16 @@
-from ._composite import WebvizComposite
+from typing import Any, Generator
+
+# pylint: disable=too-few-public-methods
+class MissingWebvizTesting:
+    def __init__(self, **kwargs: Any) -> None:
+        raise RuntimeError(
+            "webviz_config[tests] was not installed. "
+            "Please install to use the webviz testing fixtures."
+        )
+
+
+try:
+    from ._composite import WebvizComposite
+
+except ImportError:
+    WebvizComposite = MissingWebvizTesting  # type: ignore

webviz_config/testing/_plugin.py

@@ -2,20 +2,7 @@
 
 import pytest
 
-# pylint: disable=too-few-public-methods
-class MissingWebvizTesting:
-    def __init__(self, **kwargs: Any) -> None:
-        raise RuntimeError(
-            "webviz_config[tests] was not installed. "
-            "Please install to use the webviz testing fixtures."
-        )
-
-
-try:
-    from webviz_config.testing._composite import WebvizComposite
-except ImportError:
-
-    WebvizComposite = MissingWebvizTesting  # type: ignore
+from webviz_config.testing import WebvizComposite
 
 
 @pytest.fixture