Minor updates to testing documentation

Signed-off-by: Tavi Nolan <Tavi.Nolan@fmr.com>

docs/plugins/testing.md

@@ -24,7 +24,7 @@ Running an individual test (e.g. `MyComponent.test.tsx`):
 
 To run both `MyComponent.test.tsx` and `MyControl.test.tsx` suite of tests:
 
-    yarn test MyCo
+    yarn test MyComponent MyControl
 
 :::note Note
 
@@ -52,10 +52,6 @@ We use the light-weight
 [react-testing-library](https://github.com/kentcdodds/react-testing-library) to
 render React components.
 
-## Testing Utilities
-
-TODO.
-
 ## Writing Unit Tests
 
 The following principles are good guides for determining if you are writing high