Add wiki documentation

wiki/cypress-testing.md

@@ -92,3 +92,19 @@ To track what Cypress is doing while running tests, you can pass in `--config vi
 Failing screenshot artifacts (as well as Cypress logs) are generated by our Jenkins CI.
 
 TODO: Instructions on where to click to see the relevant artifact(s)/screenshots
+
+## Code coverage
+
+Cypress has been configured to automatically output Cypress code coverage to the `reports/cypress-coverage` folder. If you would prefer to turn this off locally, you can add the `--env coverage=false` flag when running your your cypress commands.
+
+To view the generated HTML reports, you can either drag the `reports/cypress-coverage/index.html` file into a browser window, or in a terminal, run `open reports/cypress-coverage/index.html` from the EUI project root.
+
+### Combined Jest & Cypress code coverage
+
+If you're working on a component that has both Cypress and Jest tests, we have a command that allows you to combine the results of both coverage reports.
+
+1. Setup: On the component(s) you're looking for final coverage #s for,
+  - Ensure you have already run `yarn test-unit --coverage` to generate a Jest report
+  - Ensure you have already run `yarn test-cypress` to generate a Cypress report
+2. Run `yarn combine-test-coverage`
+  - This should automatically open a browser window with `reports/combined-coverage/index.html`

wiki/testing.md

@@ -112,3 +112,13 @@ Component mocking relies on using the `[name].testenv.*` namespace for identific
 ### Mapping all module exports
 
 The rendered output of a mocked component is at the author's discretion, however, all public exports from a module must be preserved in the mock file. Note that this does not apply to exported TypeScript types and interfaces, which will always be derived from the original component file.
+
+## Code coverage
+
+Jest code coverage reports can be generated by running `yarn test` or `yarn test-unit` with the `--coverage` flag. Generated HTML reports are output to the `reports/` folder.
+
+To view them, you can either drag the `reports/jest-coverage/index.html` file into a browser window, or in a terminal, run `open reports/jest-coverage/index.html` from the EUI project root.
+
+We currently do not use code coverage %s in CI for automated checks or reports. Code coverage is a tool intended to help devs quickly find lines/branches that still need to be covered and determine test cases to write.
+
+> If you're working on a component that has both Cypress and Jest tests, see the [Cypress testing doc](cypress-testing.md#code-coverage) and its code coverage section for instructions on how to get a combined code coverage report.