Docs: Update tests readme to include filtering docs

tests/README.md

@@ -1,6 +1,7 @@
 # Tests
 
-Uses vitest as test runner.
+Feliz uses vitest as test runner.
+
 
 ## Run tests
 
@@ -17,7 +18,34 @@ npm run test
 ```
 
 or in watch mode:
-
 ```bash
 npm run test:watch
 ```
+
+## Run specific tests
+
+### Use `f`ocused tests
+
+You can find a helper function binding to vitest `only` test in tests/Globals:
+
+```fsharp
+let inline ftestPromise (name: string) (fn: unit -> Fable.Core.JS.Promise<unit>) = Vitest.Test.only(name, fn)
+```
+
+If you use `ftestPromise` only this test will be run, and you can adjust the focused tests during watch mode.
+
+### Use vitest test filtering
+
+To run a specific test file(s); in either **project root** or **test project root** add the filename (partial match) you want to run:
+
+For example, appending memo will check all files containing `memo`, see Vitest docs: <https://vitest.dev/guide/filtering>
+
+
+```bash
+npm run test memo
+```
+
+or in watch mode (only in test project root):
+```bash
+npm run test:watch memo
+```