Faking the mail

01 Assert the mailable, not the inbox

InvoiceMail implements ShouldQueue, so the assertion is assertQueued. assertSent is for mail that goes out during the request.

it('queues the invoice email to the billing address', function () {
    Mail::fake();

    $invoice = Invoice::factory()->issued()->create();

    $this->actingAs($invoice->team->owner)
        ->post('/invoices/'.$invoice->id.'/send')
        ->assertRedirect();

    Mail::assertQueued(InvoiceMail::class, function (InvoiceMail $mail) use ($invoice) {
        return $mail->hasTo($invoice->team->billing_email);
    });
});

Fake before the request. A fake installed afterwards does not see the mail the request already handed to the real mailer.

assertQueued does not prove the template renders. Render the mailable in one test if the view is the thing you are changing. Do not render it in every test that only cares the mail was queued.

02 Render the mailable when the view is the change

One test can build the mailable and assert the HTML. It does not send, and it does not need Mail::fake(), because nothing is handed to the mailer. assertSee() checks the invoice number the template was given.

it('renders the invoice number in the mail', function () {
    $invoice = Invoice::factory()->issued()->create();

    $html = (new InvoiceMail($invoice))->render();

    expect($html)->toContain($invoice->number);
});

Keep this test next to a view change. The queued test stays the one that proves the controller asked for the mail. A failure in render() is a broken template. A failure in assertQueued() is a controller that never dispatched it.

assertNothingQueued() belongs on the test where sending would be the bug, such as a validation failure. Mail::fake() still comes first. A test that forgets the fake and expects nothing can pass because the mailer is misconfigured, which is not the same as the controller staying quiet.