Refactor namespaces part 2 (#820)

Part 2 of refactoring effort

unittests/etl/ExtractorTests.cpp

@@ -29,6 +29,7 @@
 #include <memory>
 
 using namespace testing;
+using namespace etl;
 
 class ETLExtractorTest : public NoLoggerFixture
 {

unittests/etl/TransformerTests.cpp

@@ -30,6 +30,7 @@
 #include <memory>
 
 using namespace testing;
+using namespace etl;
 
 // taken from BackendTests
 constexpr static auto RAW_HEADER =