Erstellung typsicherer Test-Doubles mit Spy-Schnittstellen

interface DataStore {
  save(key: string, value: string): void;
  find(key: string): string | null;
}
 
class MockDataStore implements DataStore {
  public saveCalls: Array<{ key: string; value: string }> = [];
  private storage = new Map<string, string>();
 
  save(key: string, value: string): void {
    this.saveCalls.push({ key, value });
    this.storage.set(key, value);
  }
 
  find(key: string): string | null {
    return this.storage.get(key) ?? null;
  }
}
 
const mockStore = new MockDataStore();
mockStore.save("user_101", "Active");
console.assert(mockStore.saveCalls.length === 1, "Should record one save call");