Initialize unit testing and code coverage

* add: vitest configs

* added vitest scripts to package

* test coverage of src code

* initial unit testing

* added new testing workflows

* comments added, overlapping tests removed

* decouple env, tests

---------

Co-authored-by: Kevin Dang <kevinthedang_1@outlook.com>

tests/getEnvVar.test.ts

@@ -0,0 +1,50 @@
+import { describe, expect, it } from 'vitest'
+import { getEnvVar } from '../src/utils'
+
+/**
+ * getEnvVar test suite, tests the getEnvVar function
+ * 
+ * @param name name of the test suite
+ * @param fn function holding tests to run
+ */
+describe('#getEnvVar', () => {
+    // dummy set of keys
+    const keys = {
+        clientToken: 'CLIENT_TOKEN',
+    }
+
+    // set keys in environment
+    process.env['clientToken'] = keys.clientToken
+
+    // test for non-empty string
+    it('returns a non-empty string', () => {
+        expect(getEnvVar('CLIENT_TOKEN')).not.toBe('')
+    })
+
+    // test for string type
+    it('returns a string', () => {
+        expect(typeof getEnvVar('CLIENT_TOKEN')).toBe('string')
+    })
+
+    // test for distinct key
+    it('returns a distinct key', () => {
+        expect(getEnvVar('CLIENT_TOKEN')).toEqual(process.env[keys.clientToken])
+    })
+
+    // test for fallback case
+    it('returns a fallback', () => {
+        expect(getEnvVar('NON_EXISTENT_KEY', 'fallback')).toBe('fallback')
+    })
+
+    // test that all keys are consistently found
+    it('returns all keys found', () => {
+        for (const key in keys) {
+            expect(getEnvVar(key)).toEqual(keys[key])
+        }
+    })
+
+    // test that an error is thrown if key is not found
+    it('throws an error if key is not found', () => {
+        expect(() => getEnvVar('NON_EXISTENT_KEY')).toThrowError()
+    })
+})