refactor common test helpers into test/

This way we can share them with multiple tests

src/utils/index.test.ts

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: MIT
 // Copyright (c) 2020 The Pybricks Authors
 
-import { assert, hex, lookup } from '.';
+import { assert, hex } from '.';
 
 test('assert', () => {
     const assertTrue = jest.fn(() => assert(true, 'should not throw'));
@@ -16,9 +16,3 @@ test('hex', () => {
     expect(hex(1, 4)).toBe('0x0001');
     expect(hex(2, 8)).toBe('0x00000002');
 });
-
-test('lookup', () => {
-    const obj = { a: { b: { c: 'd' } } };
-    expect(lookup(obj, 'a.b.c')).toBe('d');
-    expect(lookup(obj, 'a.x.y')).toBeUndefined();
-});

src/utils/index.ts

@@ -21,18 +21,3 @@ export function assert(condition: boolean, message: string): void {
 export function hex(n: number, pad: number): string {
     return `0x${n.toString(16).padStart(pad, '0')}`;
 }
-
-/**
- * Looks up a nested property in an object.
- * @param obj The object
- * @param id The property path
- */
-export function lookup(obj: object, id: string): string | undefined {
-    const value = id
-        .split('.')
-        .reduce((pv, cv) => pv && (pv as Record<string, object>)[cv], obj);
-    if (typeof value === 'string') {
-        return value;
-    }
-    return undefined;
-}