add test cases, fix bug

Author: santerijps

jest.config.ts

@@ -0,0 +1,6 @@
+export default {
+  transform: {'^.+\\.ts?$': 'ts-jest'},
+  testEnvironment: 'node',
+  testRegex: '/tests/.*\\.(test|spec)?\\.(ts|tsx)$',
+  moduleFileExtensions: ['ts', 'tsx', 'js', 'jsx', 'json', 'node']
+};