Merge branch 'ps-rootin-tootin-troubleshootin' into 'master'

Add troubleshoot to FE guide + `nodeType` not found entry

See merge request gitlab-org/gitlab!53291

doc/development/fe_guide/index.md

@@ -121,3 +121,7 @@ Our accessibility standards and resources.
 
 Frontend internationalization support is described in [this document](../i18n/).
 The [externalization part of the guide](../i18n/externalization.md) explains the helpers/methods available.
+
+## [Troubleshooting](troubleshooting.md)
+
+Running into a Frontend development problem? Check out [this guide](troubleshooting.md) to help resolve your issue.

doc/development/fe_guide/troubleshooting.md

+---
+stage: none
+group: unassigned
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
+---
+
+# Troubleshooting
+
+Running into a problem? Maybe this will help ¯\＿(ツ)＿/¯.
+
+## Troubleshooting issues
+
+### This guide doesn't contain the issue I ran into
+
+If you run into a Frontend development issue that is not in this guide, please consider updating this guide with your issue and possible remedies. This way future adventurers can face these dragons with more success, being armed with your experience and knowedge.
+
+## Testing issues
+
+### ``Property or method `nodeType` is not defined`` but I'm not using `nodeType` anywhere
+
+This issue can happen in Vue component tests, when an expectation fails, but there is an error thrown when
+Jest tries to pretty print the diff in the console. It's been noted that using `toEqual` with an array as a
+property might also be a contributing factor.
+
+See [this video](https://youtu.be/-BkEhghP-kM) for an in-depth overview and investigation.
+
+**Remedy - Try cloning the object that has Vue watchers**
+
+```patch
+- expect(wrapper.find(ChildComponent).props()).toEqual(...);
++ expect(cloneDeep(wrapper.find(ChildComponent).props())).toEqual(...)
+```
+
+**Remedy - Try using `toMatchObject` instead of `toEqual`**
+
+```patch
+- expect(wrapper.find(ChildComponent).props()).toEqual(...);
++ expect(wrapper.find(ChildComponent).props()).toMatchObject(...);
+```
+
+Please note that `toMatchObject` actually changes the nature of the assertion and won't fail if some items are **missing** from the expectation.