#10: added unit testing guide

StringCatalogEnum/README.md

@@ -9,6 +9,7 @@ This utility converts an `xcstrings` file into a Swift `Enum`.
 - [Purpose of this utility](#purpose-of-this-utility)
 - [How to use](#how-to-use)
 - [Example](#example)
+- [Unit testing](#unit-testing)
 - [Tech stack](#tech-stack)
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
@@ -31,6 +32,10 @@ For a string with key `errorMessage` in your String Catalog, you will have a `ca
 - `SwiftUI.View(XcodeString.errorMessage.key)`
 - `let string = XcodeString.errorMessage.string`
 
+## Unit testing
+
+Before open your PR for review, make sure all unit tests are passing by running `swift test` or `make test`.
+
 ## Tech stack
 
 It is expected for the new developers to proactively research unfamiliar tech stack. It is encouraged to use `Google` or even `ChatGPT` to do your research, or even help you write some of your code, but in the end, you need to put things together to either learn how to use this utility, or make contribution. And as a contribution, you are expected to do your research about the following tech stack:
@@ -39,4 +44,4 @@ It is expected for the new developers to proactively research unfamiliar tech st
 - `Quick` and `Nimble`.
 - `Makefile` and `make`.
 
-Hint: always ask questions if you are lost, just make sure you've done your research.
+Hint: always ask questions if you are lost, just make sure you've done your research.