public function credentialsProvider()
{
$keyFilePath = __DIR__ . '/fixtures/json-key-fixture.json';
putenv("GOOGLE_APPLICATION_CREDENTIALS={$keyFilePath}");
// for application default credentials
$credentialsFetcher = $this->prophesize('Google\\Auth\\FetchAuthTokenInterface');
return [[['keyFile' => json_decode(file_get_contents($keyFilePath), true)]], [['keyFilePath' => $keyFilePath]], [['credentialsFetcher' => $credentialsFetcher->reveal()]], [[]]];
}