Prevent runtime type error due to wrong return value configuration

[sebastianbergmann]

willReturn() should raise an error when a return value is configured that does not match the stubbed method's return value.

<?php declare(strict_types=1);

class C
{
    public function m(): int
    {
        return 1;
    }
}

final class Test extends PHPUnit\Framework\TestCase
{
    public function testOne(): void
    {
        $o = $this->createMock(C::class);
        
        $o->method('m')->willReturn('not an integer');
        
        $o->m();
    }
}

Actual: TypeError when stubbed method is invoked

PHPUnit 7.1-gfafd3c555 by Sebastian Bergmann and contributors.

E                                                                   1 / 1 (100%)

Time: 68 ms, Memory: 4.00MB

There was 1 error:

1) Test::testOne
TypeError: Return value of Mock_C_06141907::m() must be of the type integer, string returned

/home/sb/Test.php:19

ERRORS!
Tests: 1, Assertions: 0, Errors: 1.