A test mechanism for testing device driver hardening includes an intercept mechanism for intercepting device driver access calls from a device driver under test and an interface for configuring the intercept mechanism to inject faults according to a determined test pattern. This mechanism enables the arbitrary introduction of typical faults. These faults may be introduced totally asynchronously and so emulate real life. A test harness module can be linked in to a test build of the driver. The test harness can intercept all of the device access calls. It mimics the normal function of these calls accessing the offset address and propagating the appropriate data. A test application is able to interpret a test script and to compare device driver responses to injected faults.