Add tests & test dependencies

jest.config.ts

@@ -0,0 +1,12 @@
+module.exports = {
+    clearMocks: true,
+    moduleFileExtensions: ['js', 'ts'],
+    roots: ['<rootDir>'],
+    testEnvironment: 'node',
+    testMatch: ['**/*.test.ts'],
+    testRunner: 'jest-circus/runner',
+    transform: {
+      '^.+\\.ts$': 'ts-jest'
+    },
+    verbose: true
+  }