update README.md regarding running tests

[skip ci]

README.md

@@ -80,8 +80,11 @@ In your custom.ini uncomment (remove the leading `;`) sign. And set `app_mode =
 
 ### Running tests
 
-- You can run backend Golang tests using "go test ./pkg/...".
-- Execute all frontend tests with "npm run test"
+#### Frontend
+Execute all frontend tests
+```bash
+$ npm run test
+```
 
 Writing & watching frontend tests (we have two test runners)
 
@@ -92,6 +95,18 @@ Writing & watching frontend tests (we have two test runners)
   - Start watcher: `npm run karma`
   - Karma+Mocha runs all files that end with the name "_specs.ts".
 
+#### Backend
+```bash
+# Run Golang tests using sqlite3 as database (default)
+$ go test ./pkg/... 
+
+# Run Golang tests using mysql as database - convenient to use /docker/block/mysql_tests
+$ GRAFANA_TEST_DB=mysql go test ./pkg/... 
+
+# Run Golang tests using postgres as database - convenient to use /docker/blocks/postgres_tests
+$ GRAFANA_TEST_DB=postgres go test ./pkg/... 
+```
+
 ## Contribute
 
 If you have any idea for an improvement or found a bug, do not hesitate to open an issue.