We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
Make test_tube optional
**Is your feature request related to a problem? Please describe.**
`test_tube` is only needed when using `TestTubeLogger`, thus it should not be an install requirement like `mlflow`.

--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `pytorch_lightning/logging/__init__.py`
Content:
```
1 from .base import LightningLoggerBase, rank_zero_only
2 from .test_tube_logger import TestTubeLogger
3 
4 try:
5     from .mlflow_logger import MLFlowLogger
6 except ModuleNotFoundError:
7     pass
8
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/pytorch_lightning/logging/__init__.py b/pytorch_lightning/logging/__init__.py
--- a/pytorch_lightning/logging/__init__.py
+++ b/pytorch_lightning/logging/__init__.py
@@ -1,6 +1,9 @@
 from .base import LightningLoggerBase, rank_zero_only
-from .test_tube_logger import TestTubeLogger
 
+try:
+    from .test_tube_logger import TestTubeLogger
+except ModuleNotFoundError:
+    pass
 try:
     from .mlflow_logger import MLFlowLogger
 except ModuleNotFoundError:

{"golden_diff": "diff --git a/pytorch_lightning/logging/__init__.py b/pytorch_lightning/logging/__init__.py\n--- a/pytorch_lightning/logging/__init__.py\n+++ b/pytorch_lightning/logging/__init__.py\n@@ -1,6 +1,9 @@\n from .base import LightningLoggerBase, rank_zero_only\n-from .test_tube_logger import TestTubeLogger\n \n+try:\n+    from .test_tube_logger import TestTubeLogger\n+except ModuleNotFoundError:\n+    pass\n try:\n     from .mlflow_logger import MLFlowLogger\n except ModuleNotFoundError:\n", "issue": "Make test_tube optional\n**Is your feature request related to a problem? Please describe.**\r\n`test_tube` is only needed when using `TestTubeLogger`, thus it should not be an install requirement like `mlflow`.\n", "before_files": [{"content": "from .base import LightningLoggerBase, rank_zero_only\nfrom .test_tube_logger import TestTubeLogger\n\ntry:\n    from .mlflow_logger import MLFlowLogger\nexcept ModuleNotFoundError:\n    pass\n", "path": "pytorch_lightning/logging/__init__.py"}], "after_files": [{"content": "from .base import LightningLoggerBase, rank_zero_only\n\ntry:\n    from .test_tube_logger import TestTubeLogger\nexcept ModuleNotFoundError:\n    pass\ntry:\n    from .mlflow_logger import MLFlowLogger\nexcept ModuleNotFoundError:\n    pass\n", "path": "pytorch_lightning/logging/__init__.py"}]}