diff --git a/src/a/component.spec.ts b/src/a/component.spec.ts
index 4e237f6..d6581ea 100644
--- a/src/a/component.spec.ts
+++ b/src/a/component.spec.ts
@@ -7,7 +7,15 @@ describe('Calculator', () => {
         component = new Calculator();
     });
 
-    it('should exist', () => {
-        expect(component).toBeTruthy();
+    it('should correctly add two numbers together', () => {
+        expect(component.add(10, 20)).toEqual(30);
+    });
+
+    it('should correctly subtract two numbers together', () => {
+        expect(component.subtract(20, 15)).toEqual(5);
+    });
+
+    it('should correctly sum a list of numbers', () => {
+        expect(component.sum([5, 10, 60])).toEqual(75);
     });
 });
diff --git a/src/b/component.spec.ts b/src/b/component.spec.ts
index 317eb62..4c82996 100644
--- a/src/b/component.spec.ts
+++ b/src/b/component.spec.ts
@@ -7,13 +7,18 @@ describe('Profile', () => {
         component = new Profile();
     });
 
-    // remember to remove the 'should exist' tests - they're just placeholders
-    it('should exist', () => {
-        expect(component).toBeTruthy();
+    it('should correctly identify when the user is an admin', () => {
+        component.user = <User>{ isAdmin: true };
+        expect(component.isAdmin).toBe(true);
     });
 
-    it('should correctly identify whether the user is an admin', () => {
-        component.user = <User>{ isAdmin: true };
-        expect(component.isAdmin).toBeDefined();
+    it('should correctly identify when the user is not an admin', () => {
+        component.user = <User>{ isAdmin: false };
+        expect(component.isAdmin).toBe(false);
+    });
+
+    it('should not be an admin if the user is undefined', () => {
+        component.user = void 0;
+        expect(component.isAdmin).toBe(false);
     });
 });
diff --git a/src/b/component.ts b/src/b/component.ts
index ac5256d..adfcedb 100644
--- a/src/b/component.ts
+++ b/src/b/component.ts
@@ -1,15 +1,12 @@
 export interface User {
     name: string;
-    isAdmin: boolean; // 👀
+    isAdmin: boolean;
 }
 
 export class Profile {
     public user?: User;
 
-    // If you have written adequate unit tests for this file,
-    // you'll find a bug! Have a go at fixing it and make sure your
-    // tests pass. I think we can use the user isAdmin field :)
     public get isAdmin(): boolean {
-        return false;
+        return !!this.user?.isAdmin;
     }
 }
diff --git a/src/c/component.spec.ts b/src/c/component.spec.ts
index 42c0b0f..4db15be 100644
--- a/src/c/component.spec.ts
+++ b/src/c/component.spec.ts
@@ -7,7 +7,29 @@ describe('SimpleBank', () => {
         component = new SimpleBank();
     });
 
-    it('should create', () => {
-        expect(component).toBeTruthy();
+    it('should throw if trying to deposit 0', () => {
+        expect(() => component.deposit(0)).toThrow();
+    });
+
+    it('should throw if trying to deposit an amount less than 0', () => {
+        expect(() => component.deposit(-5)).toThrow();
+    });
+
+    it('should increase the balance when depositing a postive number', () => {
+        component.deposit(10);
+        expect(component.balance).toEqual(10);
+    });
+
+    it('should throw if trying to withdraw 0', () => {
+        expect(() => component.deposit(0)).toThrow();
+    });
+
+    it('should throw if trying to withdraw an amount less than 0', () => {
+        expect(() => component.withdraw(-5)).toThrow();
+    });
+
+    it('should decrease the balance when withdrawing a positive number', () => {
+        component.withdraw(20);
+        expect(component.balance).toEqual(-20);
     });
 });
diff --git a/src/d/component.spec.ts b/src/d/component.spec.ts
index 427c308..bf5285f 100644
--- a/src/d/component.spec.ts
+++ b/src/d/component.spec.ts
@@ -1,24 +1,29 @@
 import { Component, User } from './component';
 
-const mockData: User = { id: 'foo', name: 'bar', age: 40 };
-
 describe('Component', () => {
     let component: Component;
     beforeEach(() => {
         component = new Component();
-        component.setUser(mockData);
     });
 
     it('should return age as undefined if no user', () => {
+        component.setUser(void 0);
+
         expect(component.age).toBeUndefined();
     });
 
     it('should correctly identify the user age', () => {
-        expect(component.age).toEqual(mockData.age);
+        const user = mockUser(50);
+        component.setUser(user);
+
+        expect(component.age).toEqual(user.age);
     });
 
     it('should increment the age of the user', () => {
+        component.setUser(mockUser(40));
+
         component.incrementAge();
+
         expect(component.age).toEqual(41);
     });
 
@@ -30,7 +35,10 @@ describe('Component', () => {
     });
 
     it('should decrement the age of the user', () => {
+        component.setUser(mockUser(40));
+
         component.decrementAge();
+
         expect(component.age).toEqual(39);
     });
 
@@ -40,4 +48,8 @@ describe('Component', () => {
             component.decrementAge();
         }).toThrow();
     });
+
+    function mockUser(age: number): User {
+        return <User>{ age };
+    }
 });
diff --git a/src/e/component.spec.ts b/src/e/component.spec.ts
index 88a4043..ab30795 100644
--- a/src/e/component.spec.ts
+++ b/src/e/component.spec.ts
@@ -1,13 +1,21 @@
-import { Engine } from './component';
+import { Engine, Status } from './component';
 
 describe('Engine', () => {
     let component: Engine;
 
     beforeEach(() => {
         component = new Engine();
+        jest.spyOn(console, 'log').mockImplementation(() => null);
     });
 
-    it('should exist', () => {
-        expect(component).toBeTruthy();
+    it('should start the engine', () => {
+        component.start();
+        expect(component.status).toBe(Status.started);
+    });
+
+    it('should stop the engine', () => {
+        component.start();
+        component.stop();
+        expect(component.status).toBe(Status.stopped);
     });
 });
diff --git a/src/e/component.ts b/src/e/component.ts
index ec3ed34..0726895 100644
--- a/src/e/component.ts
+++ b/src/e/component.ts
@@ -1,19 +1,22 @@
-export type Status = 'started' | 'stopped';
+export enum Status {
+    started,
+    stopped
+}
 
 export class Engine {
-    private _status: Status = 'stopped';
+    private _status: Status = Status.stopped;
 
-    public get status(): 'started' | 'stopped' {
+    public get status(): Status {
         return this._status;
     }
 
     public start(): void {
-        this._status = 'started';
+        this._status = Status.started;
         console.log('starting');
     }
 
     public stop(): void {
-        this._status = 'stopped';
+        this._status = Status.stopped;
         console.log('stopping');
     }
 }
diff --git a/src/f/component.spec.ts b/src/f/component.spec.ts
index 034856c..b0c19ec 100644
--- a/src/f/component.spec.ts
+++ b/src/f/component.spec.ts
@@ -1,4 +1,4 @@
-import { Shop } from './component';
+import { Car, CarColor, Shop } from './component';
 
 describe('Shop', () => {
     let component: Shop;
@@ -7,7 +7,15 @@ describe('Shop', () => {
         component = new Shop();
     });
 
-    it('should exist', () => {
-        expect(component).toBeTruthy();
+    it('should add an order to the list of orders', () => {
+        const car = mockCar('white');
+
+        component.newOrder(car, 1000);
+
+        expect(component.orders).toEqual([expect.objectContaining({ car })]);
     });
+
+    function mockCar(color: CarColor): Car {
+        return <Car>{ color, make: 'Audi' };
+    }
 });
diff --git a/src/g/component.spec.ts b/src/g/component.spec.ts
index f6a6d89..b0bbad9 100644
--- a/src/g/component.spec.ts
+++ b/src/g/component.spec.ts
@@ -1,4 +1,4 @@
-import { CustomColumnHeader } from './component';
+import { ColumnApi, ColumnHeaderParams, CustomColumnHeader } from './component';
 
 describe('CustomColumnHeader', () => {
     let component: CustomColumnHeader;
@@ -7,7 +7,65 @@ describe('CustomColumnHeader', () => {
         component = new CustomColumnHeader();
     });
 
-    it('should exist', () => {
-        expect(component).toBeTruthy();
+    it('should return undefined if no display name', () => {
+        expect(component.displayName).toBeUndefined();
     });
+
+    it('should set the display name on init', () => {
+        const params = mockParams('foo', {});
+
+        component.init(params);
+
+        expect(component.displayName).toEqual(params.headerName);
+    });
+
+    it('should not be expanded if params are undefined', () => {
+        expect(component.isExpanded).toBe(false);
+    });
+
+    it('should be expanded when column expanded is true', () => {
+        component.init(mockParams('foo', mockApi(true)));
+
+        expect(component.isExpanded).toBe(true);
+    });
+
+    it('should not be expanded when column expanded is false', () => {
+        component.init(mockParams('foo', mockApi(false)));
+
+        expect(component.isExpanded).toBe(false);
+    });
+
+    it('should not throw on toggle if params are undefined', () => {
+        expect(() => component.toggle()).not.toThrow();
+    });
+
+    it('should set expanded to true on toggle if not expanded', () => {
+        const api = mockApi(false);
+        component.init(mockParams('foo', api));
+
+        component.toggle();
+
+        expect(api.setExpanded).toHaveBeenCalledWith(true);
+    });
+
+    it('should set expanded to false on toggle if expanded', () => {
+        const api = mockApi(true);
+        component.init(mockParams('foo', api));
+
+        component.toggle();
+
+        expect(api.setExpanded).toHaveBeenCalledWith(false);
+    });
+
+    function mockApi(isExpanded: boolean): ColumnApi {
+        return <ColumnApi>{
+            isExpandable: jest.fn(),
+            isExpanded: jest.fn(() => isExpanded),
+            setExpanded: jest.fn()
+        };
+    }
+
+    function mockParams(headerName: string, api: Partial<ColumnApi>): ColumnHeaderParams {
+        return <ColumnHeaderParams>{ headerName, api };
+    }
 });
diff --git a/src/g/component.ts b/src/g/component.ts
index 7ac16bb..3a10e56 100644
--- a/src/g/component.ts
+++ b/src/g/component.ts
@@ -1,10 +1,12 @@
+export interface ColumnApi {
+    isExpandable: () => boolean;
+    isExpanded: () => boolean;
+    setExpanded: (expanded: boolean) => void;
+}
+
 export interface ColumnHeaderParams {
     headerName: string;
-    api: {
-        isExpandable: () => boolean;
-        isExpanded: () => boolean;
-        setExpanded: (expanded: boolean) => void;
-    };
+    api: ColumnApi;
 }
 
 export interface ColumnHeader {
diff --git a/src/h/component.spec.ts b/src/h/component.spec.ts
index 6003845..c04369e 100644
--- a/src/h/component.spec.ts
+++ b/src/h/component.spec.ts
@@ -1,16 +1,35 @@
-import { AccountService, UserPortal } from './component';
+import { AccountService, User, UserPortal } from './component';
 
 describe('UserPortal', () => {
     let component: UserPortal;
     let accountService: Partial<AccountService>;
+    let user: Partial<User>;
 
     beforeEach(() => {
-        accountService = {};
+        user = {};
+        accountService = {
+            doLogin: jest.fn(),
+            doLogout: jest.fn(),
+            get user() {
+                return <User>user;
+            }
+        };
         component = new UserPortal(<AccountService>accountService);
     });
 
-    it('should exist', () => {
-        expect(component).toBeTruthy();
+    it('should get the user from the account service', () => {
+        user = <User>{ id: 'foo', name: 'bar' };
+        expect(component.user).toEqual(user);
+    });
+
+    it('should get the account service to login', () => {
+        component.login();
+        expect(accountService.doLogin).toHaveBeenCalled();
+    });
+
+    it('should get the account service to logout', () => {
+        component.logout();
+        expect(accountService.doLogout).toHaveBeenCalled();
     });
 });
 
@@ -21,7 +40,20 @@ describe('AccountService', () => {
         service = new AccountService();
     });
 
-    it('should exist', () => {
-        expect(service).toBeTruthy();
+    it('should set the user on login', () => {
+        service.doLogin('bar');
+        expect(service.user).toEqual(expect.objectContaining({ id: 'bar' }));
+    });
+
+    it('should reset the user on logout', () => {
+        service.doLogin('bar');
+
+        service.doLogout();
+
+        expect(service.user).toBeUndefined();
+    });
+
+    it('should not throw on logout if user is undefined', () => {
+        expect(() => service.doLogout()).not.toThrow();
     });
 });