From Wired:

None of the Thales documents described a complete life-cycle of tests for each of the assembled battery/BCU/bus installations (main and APU)…

No records have been seen that documented the performance of the individual Li-ion battery cells in testing that involved a battery/BCU set or in a complete Model 787 airplane…

Boeing reviewed the testing done by its suppliers and thoroughly analyzed the system as a whole…

The way in which the batteries were certified for use on the 787 has been under scrutiny since the grounding. Boeing did follow the certification process carefully and ensure compliance with the rules set out by the FAA.

The whole system was not tested, it was “analyzed” (and the analysts knew what response the management wanted).

There is a simple Engineering Maxim: “If it is not tested, it does not work”.