js-tests: Update some docs related to JS tests (#1121)

src/docs/frontend/index.mdx

@@ -154,7 +154,7 @@ We are currently exploring alternatives to the `Reflux` library for future use.
   For React Testing Library (RTL) tips check out <Link to="/frontend/using-rtl/">this page</Link>.
 </Alert>
 
-Note: Your filename needs to be `.spec.jsx` or `.spec.tsx` for jest to run run it!
+Note: Your filename needs to be `.spec.tsx` for jest to run run it!
 
 We have useful fixtures defined in [setup.ts](https://github.com/getsentry/sentry/blob/master/tests/js/setup.ts) Use these! If you are defining mock data in a repetitive way, it’s probably worth adding this this file. routerContext is a particularly useful one for providing the context object that most view are written to rely on.
 
@@ -172,11 +172,6 @@ expect(wrapper.find('CommitRow')).toHaveLength(2);
 
 If you are writing jest tests, you can use a Component (and Styled Component) names as a selector. Additionally, if you need to use a DOM query selector, use `data-test-id` instead of a class name. We currently don’t, but it is something we can use babel to strip out during the build process.
 
-### Undefined `theme` properties in tests
-
-Instead of using `mount()` from `enzyme` ...use this: `import {mountWithTheme} from 'sentry-test/enzyme'` so that the component under test gets wrapped with a [`<ThemeProvider>`](https://emotion.sh/docs/theming).
-
-
 ## Babel Syntax Plugins
 We have decided to only use ECMAScript proposals that are in stage 3 (or later) (See [TC39 Proposals](https://github.com/tc39/proposals)). Additionally, because we are migrating to typescript, we will align with what their compiler supports.
 The only exception to this are decorators.

src/docs/testing.mdx

@@ -268,7 +268,8 @@ yarn test tests/js/spec/views/issueList/overview.spec.js
 ### API Fixtures
 
 Because our Jest tests run without an API we have a variety of fixture builders available to help generate
-API response payloads. The `TestStubs` global includes all the fixture functions in `tests/js/sentry-test/fixtures/`.
+API response payloads. They are available for import with the alias `sentry-fixture/*`. New fixtures can be created 
+inside of `sentry/fixtures/js-stubs/`.
 
 You should also use `MockApiClient.addMockResponse()` to set responses for API calls your components will make. Failing
 to mock an endpoint will result in tests failing.