Add unit tests for decodeJWT function to validate JWT decoding (#55)

Signed-off-by: Joye Lin <y12studio@gmail.com>

Author: y12studio

src/test/jwt.spec.ts

@@ -14,6 +14,32 @@ describe('JWT', () => {
     expect(jwt.payload).toEqual({ foo: 'bar' });
   });
 
+  test('returns decoded JWT when correct JWT string is provided', () => {
+    // Two objects are created separately, the first: { alg: 'HS256', typ: 'JWT' } represents a JWT Header and the second: { sub: '1234567890', name: 'John Doe' } represents a JWT Payload.
+    // These objects are turned into strings with JSON.stringify. The resulting strings are encoded with base64 encoding using Buffer.from(string).toString('base64').
+    // These base64 encoded strings are concatenated with a period (.) between them, following the structure of a JWT, which is composed of three Base64-URL strings separated by dots (header.payload.signature).
+    // A 'signature' string is added at the end to represent a JWT signature.
+    // So, the jwt variable ends up being a string with the format of a base64Url encoded Header, a period, a base64Url encoded Payload, another period, and a 'signature' string. 
+    // It's important to note that the 'signature' here is just a placeholder string and not an actual cryptographic signature generated from the header and payload data.
+    const jwt = `${Buffer.from(JSON.stringify({ alg: 'HS256', typ: 'JWT' })).toString('base64')}.${Buffer.from(JSON.stringify({ sub: '1234567890', name: 'John Doe' })).toString('base64')}.signature`;
+    const result = Jwt.decodeJWT(jwt);
+    expect(result).toEqual({
+      header: { alg: 'HS256', typ: 'JWT' },
+      payload: { sub: '1234567890', name: 'John Doe' },
+      signature: 'signature',
+    });
+  });
+
+  test('throws an error when JWT string is not correctly formed', () => {
+    const jwt = 'abc.def';
+    expect(() => Jwt.decodeJWT(jwt)).toThrow('Invalid JWT as input');
+  });
+
+  test('throws an error when JWT parts are missing', () => {
+    const jwt = `${Buffer.from(JSON.stringify({ alg: 'HS256', typ: 'JWT' })).toString('base64')}`;
+    expect(() => Jwt.decodeJWT(jwt)).toThrow('Invalid JWT as input');
+  });
+
   test('set', async () => {
     const jwt = new Jwt();
     jwt.setHeader({ alg: 'EdDSA' });