Docs for 5195 from main repository (#7)

Co-authored-by: Peter Sobolewski <76622105+psobolewskiPhD@users.noreply.github.com>
Co-authored-by: Melissa Weber Mendonça <melissawm@gmail.com>

Author: 3 people

docs/plugins/debug_plugins.md

@@ -8,6 +8,7 @@ When developing plugins in napari, you may encounter mistakes or bugs in your co
 4. Reloading code during plugin development.
 5. Isolating issues from napari.
 6. Logging and debug messages.
+7. Debugging segfaults/memory violation errors 
 
 ## Debugging plugin start-up issues
 
@@ -287,4 +288,24 @@ DEBUG: 20/09/2022 05:59:23 PM The input string was (logging): fast
 'You entered fast!'
 ```
 
-The full code changes and new files after applying the changes to the plugin in each step of the examples are [here](https://github.com/seankmartin/napari-plugin-debug/tree/full_code/napari-simple-reload).
+
+The full code changes and new files after applying the changes to the plugin in each step of the examples are [here](https://github.com/seankmartin/napari-plugin-debug/tree/full_code/napari-simple-reload).
+
+## Debugging segfaults/memory violation errors
+
+If napari crashes with a segfault or memory violation error when using your plugin
+it may be connected with setting some viewer/layers properties outside main thread.
+Because of the limitations of the Qt library, such interactions with napari may lead to a crash. 
+
+To test if this is the case, you can use the `NAPARI_ENSURE_PLUGIN_MAIN_THREAD` environment variable to help debug the issue.
+
+Set the environement variable: `NAPARI_ENSURE_PLUGIN_MAIN_THREAD=1`, then start napari and run your plugin.
+
+```bash
+NAPARI_ENSURE_PLUGIN_MAIN_THREAD=1 napari
+```
+
+Next, start using your plugin and observe if 
+`RuntimeError("Setting attributes on a napari object is only allowed from the main Qt thread.")`
+occurred. If so, then you need to make sure that all of your plugin code that interacts with napari structures is executed 
+in the main thread. For more details you could read the [multithreading](https://napari.org/stable/guides/threading.html) section of the documentation.

docs/plugins/test_deploy.md

@@ -12,23 +12,26 @@ We recommend using
 [pytest](https://docs.pytest.org/en/6.2.x/getting-started.html) for testing your
 plugin. Aim for [100% test coverage](./best_practices.md#how-to-check-test-coverage)!
 
-### The `make_napari_viewer` fixture
+### The `make_napari_viewer_proxy` fixture
 
 Testing a napari `Viewer` requires some setup and teardown each time.  We have
 created a [pytest fixture](https://docs.pytest.org/en/6.2.x/fixture.html) called
-`make_napari_viewer` that you can use (this requires that you have napari
+`make_napari_viewer_proxy` that you can use (this requires that you have napari
 installed in your environment).
 
 To use a fixture in pytest, you simply include the name of the fixture in the
 test parameters (oddly enough, you don't need to import it!).  For example, to
 create a napari viewer for testing:
 
 ```
-def test_something_with_a_viewer(make_napari_viewer):
-    viewer = make_napari_viewer()
+def test_something_with_a_viewer(make_napari_viewer_proxy):
+    viewer = make_napari_viewer_proxy()
     ...  # carry on with your test
 ```
 
+If you embed the viewer in your own application and need to access private attributes,
+you can use the `make_napari_viewer` fixture.
+
 ### Prefer smaller unit tests when possible
 
 The most common issue people run into when designing tests for napari plugins is