PHP Unit 4.3 breaks tests

The MockObject code changed in PHP Unit 4.3:

1) Bitpay\Client\ClientTest::testCreateInvoiceWithError
Argument 1 passed to PHPUnit_Framework_MockObject_Builder_InvocationMocker::will() must implement interface PHPUnit_Framework_MockObject_Stub, string given, called in /home/travis/build/bitpay/php-bitpay-client/tests/Bitpay/Client/ClientTest.php on line 133 and defined
/home/travis/build/bitpay/php-bitpay-client/tests/Bitpay/Client/ClientTest.php:133