Strict Mocks

Every mock instance is wrapped in a Proxy that throws a descriptive error when you read a property that is not implemented, instead of silently returning undefined:

Property "internalPlugins" is not mocked in App. To override, assign a value first: mock.internalPlugins = ...

This turns “the mock quietly returned undefined and the assertion passed for the wrong reason” into a failure you can read.

Overriding behavior

The strict proxy is fully override-friendly. Assign a value and subsequent reads just work:

// Spy on an existing method
vi.spyOn(app.vault, 'read').mockResolvedValue('custom content');

// Batch-extend with Object.assign
Object.assign(app, { commands: { addCommand: vi.fn() } });

Accessing unimplemented properties

Properties the mock does not implement (such as app.internalPlugins) throw at runtime, and you make them available by assigning a value first:

app.internalPlugins = { manifests: {} };

But internalPlugins is not declared in obsidian.d.ts, so TypeScript will not compile that assignment on its own. The options, best to worst:

1. Use obsidian-typings (recommended) — install obsidian-typings, which declares the full internal API. The assignment compiles with no extra work. See Using with obsidian-typings.

2. Manual module augmentation (recommended) — declare only what you need:

declare module 'obsidian' {
  interface App {
    internalPlugins: { manifests: Record<string, unknown> };
  }
}

app.internalPlugins = { manifests: {} };

3. Cast to Record<string, unknown> (less recommended) — a quick one-off escape hatch that still catches typos in the value:

(app as Record<string, unknown>).internalPlugins = { manifests: {} };

4. as any / @ts-expect-error / @ts-ignore (not recommended) — suppresses all type checking and hides real errors:

(app as any).internalPlugins = { manifests: {} };

// @ts-expect-error -- accessing internal API
app.internalPlugins = { manifests: {} };