Update the contributing guide

Author: kossnocorp

Diff for: CONTRIBUTING.md

@@ -6,30 +6,50 @@ Please use [Prettier](https://prettier.io/) to format the code.
 
 ## Tests
 
-As Typesaurus itself, its tests work both in browser and Node.js. Typesaurus tests connect to a real database, so to run them, you need to prepare a Firebase project and point the suite to the project. See [How to set up tests?](#how-to-set-up-tests) for more details.
+### Unit tests
 
-### How to run tests?
+Before running unit tests for the first time, you need to download the Firestore emulator by running the command:
+
+```bash
+make test-setup
+```
 
 To run the tests:
 
 ```bash
-# Run tests both in Node.js and browser:
+# Run tests once
 make test
 
+# Run tests in the watch mode
+make test-watch
+```
+
+### System tests
+
+As Typesaurus itself, its tests work both in browser and Node.js. Typesaurus system tests connect to a real database, so to run them, you need to prepare a Firebase project and point the suite to the project. See [How to set up tests?](#how-to-set-up-system-tests) for more details.
+
+#### How to run system tests?
+
+To run the tests:
+
+```bash
+# Run tests both in Node.js and browser:
+make test-system
+
 # Run only Node.js tests:
-make test-node
+make test-system-node
 
 # Run Node.js tests in the watch mode:
-make test-node-watch
+make test-system-node-watch
 
 # Run only browser tests:
-make test-node
+make test-system-browser
 
 # Run browser tests in the watch mode:
-make test-node-watch
+make test-system-browser-watch
 ```
 
-### How to set up tests?
+#### How to set up system tests?
 
 1. First of all, [create a Firebase project](https://console.firebase.google.com/) and [enable Firestore](https://console.firebase.google.com/project/_/storage).
 

Diff for: Makefile

@@ -10,6 +10,9 @@ test:
 test-watch:
 	${BIN}/firebase emulators:exec --only firestore "${BIN}/jest --env node --watch"
 
+test-setup:
+	${BIN}/firebase setup:emulators:firestore
+
 test-system: test-system-node test-system-browser
 
 test-system-node: