Add instructions for running tests in Windows / WSL (#348)

README.md

@@ -155,3 +155,26 @@ To build types:
 To run tests. Note: Headless tests will mostly fail due to lack of headless canvas pixel detection support. Use VM testing or your browser.
 
     npm test
+
+### Windows 10 WSL Testing
+*This is info for wsl version 1. v2 seems to be [different](https://dev.to/davelsan/comment/nnf5).*
+
+- `CHROME_BIN` needs to be set to the location of your Google Chrome exe in Windows. (e.g. `/mnt/c/Program Files (x86)/Google/Chrome/Application/chrome.exe`)
+   *in WSL, `export CHROME_BIN='path/to/chrome'`*
+- Chrome needs access to [karma's temp folder](https://stackoverflow.com/a/56204265/292067).
+  - Create a `tmp` folder on the same Windows drive as your repo.
+  - set `TEMP` to a folder that exists on the same Windows drive as your repo. (matching capitalization probably matters)
+    *in WSL, `export TEMP='/Temp/karma'`, if your repo is on drive C, then create folder C:\Temp\karma*
+- karma.conf.js needs to be edited
+  - Change the browser from `ChromeHeadless` to `Chrome`
+  - Modify to run ChromeHeadless without sandboxing. This is not ideal, but it seems to be necessary in [WSL](https://github.com/microsoft/WSL/issues/3282) and [Linux containers](https://docs.travis-ci.com/user/chrome#sandboxing) ([see also](https://github.com/karma-runner/karma-chrome-launcher/issues/158#issuecomment-339265457))
+    - Add a custom launcher
+      ```
+      customLaunchers: {
+        ChromeHeadlessNoSandbox: {
+            base: 'ChromeHeadless',
+            flags: ['--no-sandbox']
+        }
+      }
+      ```
+    - Change the browser from `ChromeHeadless` to `ChromeHeadlessNoSandbox`