docs: enhance TESTING.md troubleshooting section with detailed Playwright command explanation

Add comprehensive breakdown of the --headed test debugging command, explaining each parameter and its purpose for visual test debugging. Resolves "New offers for another user" test debugging workflow.

test-playwright/TESTING.md

@@ -88,3 +88,18 @@ firefox --no-remote --profile $(realpath profiles/dev2) --devtools --new-window
 1. Identity Errors:
    - "No keys for ID" errors may occur when current account was erased
    - Account switching can cause issues with erased accounts
+
+2. If you find yourself wanting to see the testing process try something like this:
+
+```
+npx playwright test -c playwright.config-local.ts test-playwright/60-new-activity.spec.ts --grep "New offers for another user" --headed
+```
+
+This command allows you to:
+- **Run a specific test file**: `test-playwright/60-new-activity.spec.ts`
+- **Filter to a specific test**: `--grep "New offers for another user"` runs only tests with that name
+- **See the browser**: `--headed` opens the browser window so you can watch the test execute
+- **Use local config**: `-c playwright.config-local.ts` uses the local configuration file
+
+This is useful when you want to observe the testing process visually rather than running tests in headless mode. It's particularly helpful for debugging test failures or understanding how the application behaves during automated testing.
+