Add unit tests for MMKV storage functionality

Author: riteshshukla04

example/__tests__/MMKV.test.ts

@@ -0,0 +1,36 @@
+import { createMMKV } from 'react-native-mmkv';
+describe('Example test', () => {
+  let storage: MMKV;
+
+  beforeAll(() => {
+    storage = createMMKV();
+  });
+
+  it('functions correctly', () => {
+    storage.set('testString', 'value');
+    storage.set('testNumber', 99);
+    storage.set('testBoolean', false);
+
+    expect(storage.getString('testString')).toStrictEqual('value');
+    expect(storage.getNumber('testString')).toBeUndefined();
+    expect(storage.getBoolean('testString')).toBeUndefined();
+    expect(storage.getString('testNumber')).toBeUndefined();
+    expect(storage.getNumber('testNumber')).toStrictEqual(99);
+    expect(storage.getBoolean('testNumber')).toBeUndefined();
+    expect(storage.getString('testBoolean')).toBeUndefined();
+    expect(storage.getNumber('testBoolean')).toBeUndefined();
+    expect(storage.getBoolean('testBoolean')).toStrictEqual(false);
+    expect(storage.getAllKeys()).toEqual(
+      expect.arrayContaining(['testString', 'testNumber', 'testBoolean'])
+    );
+
+    storage.remove('testBoolean');
+    expect(storage.contains('testBoolean')).toBeFalsy();
+    expect(storage.getAllKeys()).toEqual(
+      expect.arrayContaining(['testString', 'testNumber'])
+    );
+
+    storage.clearAll();
+    expect(storage.toString()).toStrictEqual('MMKV (mmkv.default): []');
+  });
+});