can't stub getMessage method of interface that extends Throwable

[jacekkarczmarczyk]

Q	A
PHPUnit version	9.3.10
PHP version	7.4
Installation Method	Composer

Summary

$mock->method('getMessage') fails for interface that extends Throwable

Current behavior

testRealThrowable fails with error:

Trying to configure method "getMessage" which cannot be configured because it does not exist, has not been specified, is final, or is static

How to reproduce

<?php

declare(strict_types=1);

use PHPUnit\Framework\TestCase;
use Throwable;

interface Bar extends Throwable
{
    public function foo();
}

interface FakeThrowable
{
    public function getMessage();
}

interface Baz extends FakeThrowable
{
    public function foo();
}

final class FooTest extends TestCase
{
    public function testFakeThrowable(): void
    {
        $mock = $this->createMock(Baz::class);
        $mock->method('foo')->willReturn(null);
        $mock->method('getMessage')->willReturn(null);
        $this->assertTrue(true);
    }

    public function testRealThrowable(): void
    {
        $mock = $this->createMock(Bar::class);
        $mock->method('foo')->willReturn(null);
        $mock->method('getMessage')->willReturn(null);
        $this->assertTrue(true);
    }
}

Expected behavior

Both tests pass

[thicolares]

@jacekkarczmarczyk: it happens because when PHPUnit detects you're mocking an interface that extends Throwable, PHPUnit returns an Exception mock instead [1].

But on Exception, getMessage is final therefore you see the error.

[1] You may want to read this thread that was created based on this bug report.