Document testing options

backend/src/emails/README.md

@@ -24,3 +24,35 @@ The full `pug` documentation you'll find here:
 In case we are sending many emails in the future there is the possibility to cache the `pug` templates:
 
 - [cache-pug-templates](https://github.com/ladjs/cache-pug-templates)
+
+## Testing
+
+To test your send emails you have different possibilities:
+
+### In General
+
+To send emails to yourself while developing set in `.env` the value `EMAIL_TEST_MODUS=true` and `EMAIL_TEST_RECEIVER` to your preferred email address.
+
+### Unit Or Integration Tests
+
+To change the behavior to show previews etc. you have the following options to be set in `sendEmailTranslated.ts` on creating the email object:
+
+```js
+  const email = new Email({
+    …
+    // send emails in development/test env:
+    send: true,
+    …
+    // to open send emails in the browser
+    preview: true,
+    // or
+    // to open send emails in a specific the browser
+    preview: {
+      open: {
+        app: 'firefox',
+        wait: false,
+      },
+    },
+    …
+  })
+```