It was an embedded software running on a specific hardware. Software was consisting of different modules for each task. The functionality that I was testing was related to two different modules which are written by two different developers. Required functionality was not working and test was failing consistently. Then, we debugged the Module-1 with Developer-1, Module-1 seemed to work properly. Then, we debugged the Module-2 with Developer-2, Module-2 also seemed to work surprisingly. Of course, each developer was blaming the other developer for the fault : ) Then I suspected about my own test case and re-reviewed and inspected it again, but test case also seemed as OK. Afterwards, we suspected about the software testing tool and debugged it with the developer of the test tool. Not surprisingly, test tool also seemed to work properly : ). Ooopsss. What is next? The next suspicious guy was the data buses between test tool and the software/hardware. Then we checked data