diff --git a/app.mock.test.js b/app.mock.test.js
new file mode 100644
index 0000000..860b81a
--- /dev/null
+++ b/app.mock.test.js
@@ -0,0 +1,181 @@
+
+const createApp = require('./app');
+const request = require('supertest');
+
+jest.mock('./validation/validateEmail', () => {
+    return jest.fn((email) => {
+        return email === 'student@example.com';
+    });
+});
+
+const validateUsername = require('./validation/validateUsername');
+const validatePassword = require('./validation/validatePassword');
+const validateEmail = require('./validation/validateEmail');
+
+const app = createApp(validateUsername, validatePassword, validateEmail);
+
+describe('given correct username and password', () => {
+    test('return status 200', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'Username',
+            password: 'Password123',
+            email: 'student@example.com'
+        });
+        expect(response.statusCode).toBe(200);
+    });
+
+    test('returns userId', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'Username',
+            password: 'Password123',
+            email: 'student@example.com'
+        });
+        expect(response.body.userId).toBeDefined();
+    });
+
+    test('response content type should be JSON', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'Username',
+            password: 'Password123',
+            email: 'student@example.com'
+        });
+        expect(response.headers['content-type']).toMatch(/json/);
+    });
+
+    test('response message should be Valid User', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'Username',
+            password: 'Password123',
+            email: 'student@example.com'
+        });
+        expect(response.body).toEqual({ userId: "1", message: "Valid User" });
+    });
+
+    test('user id value should be valid', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'Username',
+            password: 'Password123',
+            email: 'student@example.com'
+        });
+        expect(response.body.userId).toBe("1");
+    });
+});
+
+describe('given incorrect or missing username and password', () => {
+    test('return status 400', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'user',
+            password: 'password',
+            email: 'not-an-email'
+        });
+        expect(response.statusCode).toBe(400);
+    });
+
+    test('response message should be Invalid User', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'er',
+            password: 'Password123',
+            email: 'student@example.com'
+        });
+        expect(response.body).toEqual({ error: "Invalid User" });
+    });
+
+    test('response should not have userId', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'er',
+            password: 'Password123',
+            email: 'student@example.com'
+        });
+        expect(response.body.userId).toBeUndefined();
+    });
+
+    test('username too short', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'abc',
+            password: 'Password1',
+            email: 'student@example.com'
+        });
+        expect(response.body.error).toBe('Invalid User');
+    });
+
+    test('username with invalid characters', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'Invalid@Name',
+            password: 'Password1',
+            email: 'student@example.com'
+        });
+        expect(response.body.error).toBe('Invalid User');
+    });
+
+    test('password too short', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'ValidUsername',
+            password: 'Pass1',
+            email: 'student@example.com'
+        });
+        expect(response.body.error).toBe('Invalid User');
+    });
+
+    test('password missing uppercase', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'ValidUsername',
+            password: 'password1',
+            email: 'student@example.com'
+        });
+        expect(response.body.error).toBe('Invalid User');
+    });
+
+    test('password missing lowercase', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'ValidUsername',
+            password: 'PASSWORD1',
+            email: 'student@example.com'
+        });
+        expect(response.body.error).toBe('Invalid User');
+    });
+
+    test('password contains special characters', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'ValidUsername',
+            password: 'Password1!',
+            email: 'student@example.com'
+        });
+        expect(response.body.error).toBe('Invalid User');
+    });
+
+    test('email missing @', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'ValidUsername',
+            password: 'Password1',
+            email: 'studentexample.com'
+        });
+        expect(response.body.error).toBe('Invalid User');
+    });
+
+    test('email invalid domain', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'ValidUsername',
+            password: 'Password1',
+            email: 'student@example'
+        });
+        expect(response.body.error).toBe('Invalid User');
+    });
+
+    test('password missing', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'ValidUsername',
+            password: '',
+            email: 'student@example.com'
+        });
+        expect(response.body.error).toBe('Invalid User');
+    });
+
+    test('username missing', async () => {
+        const response = await request(app).post('/users').send({
+            username: '',
+            password: 'Password1',
+            email: 'student@example.com'
+        });
+        expect(response.body.error).toBe('Invalid User');
+    });
+});
\ No newline at end of file
diff --git a/app.test.js b/app.test.js
index f1b561d..4d4366e 100644
--- a/app.test.js
+++ b/app.test.js
@@ -3,6 +3,7 @@ const request = require('supertest')
 const validateUsername = require('./validation/validateUsername')
 const validatePassword = require('./validation/validatePassword')
 const validateEmail = require('./validation/validateEmail')
+const { response } = require('express')
 
 const app = createApp(validateUsername, validatePassword, validateEmail)
 
@@ -26,8 +27,36 @@ describe('given correct username and password', () => {
     })
 
     // test response content type?
+    test('response content type should be JSON', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'Username',
+            password: 'Password123',
+            email: 'student@example.com'
+        })
+
+        expect(response.headers['content-type']).toMatch(/json/)
+    })
+
     // test response message
+    test('response message should be Valid User', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'Username',
+            password: 'Password123',
+            email: 'student@example.com'
+        })
+        expect(response.body).toEqual({ userId: "1", message: "Valid User" })
+    })
+
+
     // test response user id value
+    test('user id value should be valid', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'Username',
+            password: 'Password123',
+            email: 'student@example.com'
+        })
+        expect(response.body.userId).toBe("1")
+    })
     // ...
 })
 
@@ -42,8 +71,122 @@ describe('given incorrect or missing username and password', () => {
     })
 
     // test response message
+    test('response message should be Invalid User', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'er',
+            password: 'Password123',
+            email: 'student@example.com'
+        })
+        expect(response.body).toEqual({ error: "Invalid User" })
+    })
     // test that response does NOT have userId
+    test('response should not have userId', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'er',
+            password: 'Password123',
+            email: 'student@example.com'
+        })
+        expect(response.body.userId).toBeUndefined();
+    })
     // test incorrect username or password according to requirements
+    test('username too short', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'abc',        // too short (<6)
+            password: 'Password1',
+            email: 'student@example.com'
+        })
+
+        expect(response.body.error).toBe('Invalid User')
+    })
+
+    test('username with invalid characters', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'Invalid@Name',
+            password: 'Password1',
+            email: 'student@example.com'
+        })
+
+        expect(response.body.error).toBe('Invalid User')
+    })
+
+    test('password too short', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'ValidUsername',
+            password: 'Pass1',  
+            email: 'student@example.com'
+        })
+
+        expect(response.body.error).toBe('Invalid User')
+    })
+
+    test('password missing uppercase', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'ValidUsername',
+            password: 'password1', 
+            email: 'student@example.com'
+        })
+
+        expect(response.body.error).toBe('Invalid User')
+    })
+
+    test('password missing lowercase', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'ValidUsername',
+            password: 'PASSWORD1',
+            email: 'student@example.com'
+        })
+
+        expect(response.body.error).toBe('Invalid User')
+    })
+
+    test('password contains special characters', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'ValidUsername',
+            password: 'Password1!',
+            email: 'student@example.com'
+        })
+
+        expect(response.body.error).toBe('Invalid User')
+    })
+
+    test('email missing @', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'ValidUsername',
+            password: 'Password1',
+            email: 'studentexample.com'
+        })
+
+        expect(response.body.error).toBe('Invalid User')
+    })
+
+    test('email invalid domain', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'ValidUsername',
+            password: 'Password1',
+            email: 'student@example'
+        })
+
+        expect(response.body.error).toBe('Invalid User')
+    })
     // test missing username or password
+    test('password missing', async () => {
+        const response = await request(app).post('/users').send({
+            username: 'ValidUsername',
+            password: '',
+            email: 'student@example.com'
+        })
+
+        expect(response.body.error).toBe('Invalid User')
+    })
+
+    test('username missing', async () => {
+        const response = await request(app).post('/users').send({
+            username: '',
+            password: 'Password1',
+            email: 'student@example.com'
+        })
+
+        expect(response.body.error).toBe('Invalid User')
+    })
     // ...
 })
\ No newline at end of file