Added tests for the CompositeWriter
Added tests for the CompositeWriter


Former-commit-id: 106436e44508e30d4252727e54fad783a80b25a0 [formerly 2510d6cbf436f31e791c7845064c3d5653890959]
Former-commit-id: 71670ae0097bc4d927ee2d56032be55a49b550a5
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine