Submitting forms using spies

In this section, you’ll hand-craft a reusable spy function and adjust your tests to get them back into AAA order.

Here’s a reminder of how one of those tests looked, from the CustomerForm test suite. It’s complicated by the fact it’s wrapped in a test generator, but you can ignore that bit for now—it’s the test content that’s important:

const itSubmitsExistingValue = (fieldName, value) =>
  it("saves existing value when submitted", () => {
    expect.hasAssertions();
    const customer = { [fieldName]: value };
    render(
      <CustomerForm
        original={customer}
        onSubmit={(props) =>
          expect(props[fieldName]).toEqual(value)
 ...