diff --git a/src/servers/data/index.ts b/src/servers/data/index.ts
index 61f86009..0a89ae2c 100644
--- a/src/servers/data/index.ts
+++ b/src/servers/data/index.ts
@@ -35,3 +35,6 @@ export const isReachableServer = (server: SelectedServer): server is ReachableSe
 
 export const isServerWithId = (server: SelectedServer | ServerWithId): server is ServerWithId =>
   !!server?.hasOwnProperty('id');
+
+export const isNotFoundServer = (server: SelectedServer): server is NotFoundServer =>
+  !!server?.hasOwnProperty('serverNotFound');
diff --git a/src/servers/helpers/withSelectedServer.tsx b/src/servers/helpers/withSelectedServer.tsx
index 2215ded3..f308d6e0 100644
--- a/src/servers/helpers/withSelectedServer.tsx
+++ b/src/servers/helpers/withSelectedServer.tsx
@@ -1,7 +1,7 @@
 import React, { FC, useEffect } from 'react';
 import { RouteChildrenProps } from 'react-router';
 import Message from '../../utils/Message';
-import { isReachableServer, SelectedServer } from '../data';
+import { isNotFoundServer, SelectedServer } from '../data';
 
 interface WithSelectedServerProps extends RouteChildrenProps<{ serverId: string }> {
   selectServer: (serverId: string) => void;
@@ -21,7 +21,7 @@ export const withSelectedServer = (WrappedComponent: FC<WithSelectedServerProps>
     return <Message loading />;
   }
 
-  if (!isReachableServer(selectedServer)) {
+  if (isNotFoundServer(selectedServer)) {
     return <ServerError />;
   }
 
diff --git a/src/utils/services/ColorGenerator.js b/src/utils/services/ColorGenerator.ts
similarity index 56%
rename from src/utils/services/ColorGenerator.js
rename to src/utils/services/ColorGenerator.ts
index 1a15f2a4..5f79b0b8 100644
--- a/src/utils/services/ColorGenerator.js
+++ b/src/utils/services/ColorGenerator.ts
@@ -1,20 +1,21 @@
 import PropTypes from 'prop-types';
 import { rangeOf } from '../utils';
+import LocalStorage from './LocalStorage';
 
 const HEX_COLOR_LENGTH = 6;
 const { floor, random } = Math;
 const letters = '0123456789ABCDEF';
-const buildRandomColor = () =>
-  `#${rangeOf(HEX_COLOR_LENGTH, () => letters[floor(random() * letters.length)]).join('')}`;
-const normalizeKey = (key) => key.toLowerCase().trim();
+const buildRandomColor = () => `#${rangeOf(HEX_COLOR_LENGTH, () => letters[floor(random() * letters.length)]).join('')}`;
+const normalizeKey = (key: string) => key.toLowerCase().trim();
 
 export default class ColorGenerator {
-  constructor(storage) {
-    this.storage = storage;
-    this.colors = this.storage.get('colors') || {};
+  private readonly colors: Record<string, string>;
+
+  public constructor(private readonly storage: LocalStorage) {
+    this.colors = this.storage.get<Record<string, string>>('colors') || {};
   }
 
-  getColorForKey = (key) => {
+  public readonly getColorForKey = (key: string) => {
     const normalizedKey = normalizeKey(key);
     const color = this.colors[normalizedKey];
 
@@ -26,7 +27,7 @@ export default class ColorGenerator {
     return color;
   };
 
-  setColorForKey = (key, color) => {
+  public readonly setColorForKey = (key: string, color: string) => {
     const normalizedKey = normalizeKey(key);
 
     this.colors[normalizedKey] = color;
@@ -36,6 +37,7 @@ export default class ColorGenerator {
   };
 }
 
+/** @deprecated Use ColorGenerator class instead */
 export const colorGeneratorType = PropTypes.shape({
   getColorForKey: PropTypes.func,
   setColorForKey: PropTypes.func,
diff --git a/test/servers/EditServer.test.js b/test/servers/EditServer.test.js
index 0dd0f155..366dd24f 100644
--- a/test/servers/EditServer.test.js
+++ b/test/servers/EditServer.test.js
@@ -16,8 +16,6 @@ describe('<EditServer />', () => {
     name: 'name',
     url: 'url',
     apiKey: 'apiKey',
-    printableVersion: 'v1.2.0',
-    version: '1.2.0'
   };
 
   beforeEach(() => {
diff --git a/test/utils/services/ColorGenerator.test.js b/test/utils/services/ColorGenerator.test.ts
similarity index 87%
rename from test/utils/services/ColorGenerator.test.js
rename to test/utils/services/ColorGenerator.test.ts
index 71546d17..990b268e 100644
--- a/test/utils/services/ColorGenerator.test.js
+++ b/test/utils/services/ColorGenerator.test.ts
@@ -1,16 +1,16 @@
+import { Mock } from 'ts-mockery';
 import ColorGenerator from '../../../src/utils/services/ColorGenerator';
+import LocalStorage from '../../../src/utils/services/LocalStorage';
 
 describe('ColorGenerator', () => {
-  let colorGenerator;
-  const storageMock = {
+  let colorGenerator: ColorGenerator;
+  const storageMock = Mock.of<LocalStorage>({
     set: jest.fn(),
     get: jest.fn(),
-  };
+  });
 
   beforeEach(() => {
-    storageMock.set.mockReset();
-    storageMock.get.mockReset();
-
+    jest.clearAllMocks();
     colorGenerator = new ColorGenerator(storageMock);
   });
 
diff --git a/test/utils/services/Storage.test.js b/test/utils/services/Storage.test.ts
similarity index 64%
rename from test/utils/services/Storage.test.js
rename to test/utils/services/Storage.test.ts
index ec427015..e7de6771 100644
--- a/test/utils/services/Storage.test.js
+++ b/test/utils/services/Storage.test.ts
@@ -1,16 +1,14 @@
+import { Mock } from 'ts-mockery';
 import LocalStorage from '../../../src/utils/services/LocalStorage';
 
 describe('LocalStorage', () => {
-  const localStorageMock = {
-    getItem: jest.fn((key) => key === 'shlink.foo' ? JSON.stringify({ foo: 'bar' }) : null),
-    setItem: jest.fn(),
-  };
-  let storage;
+  const getItem = jest.fn((key) => key === 'shlink.foo' ? JSON.stringify({ foo: 'bar' }) : null);
+  const setItem = jest.fn();
+  const localStorageMock = Mock.of<Storage>({ getItem, setItem });
+  let storage: LocalStorage;
 
   beforeEach(() => {
-    localStorageMock.getItem.mockClear();
-    localStorageMock.setItem.mockReset();
-
+    jest.clearAllMocks();
     storage = new LocalStorage(localStorageMock);
   });
 
@@ -20,15 +18,15 @@ describe('LocalStorage', () => {
 
       storage.set('foo', value);
 
-      expect(localStorageMock.setItem).toHaveBeenCalledTimes(1);
-      expect(localStorageMock.setItem).toHaveBeenCalledWith('shlink.foo', JSON.stringify(value));
+      expect(setItem).toHaveBeenCalledTimes(1);
+      expect(setItem).toHaveBeenCalledWith('shlink.foo', JSON.stringify(value));
     });
   });
 
   describe('get', () => {
     it('fetches item from local storage', () => {
       storage.get('foo');
-      expect(localStorageMock.getItem).toHaveBeenCalledTimes(1);
+      expect(getItem).toHaveBeenCalledTimes(1);
     });
 
     it('returns parsed value when requested value is found in local storage', () => {