It seems difficult to test. Being difficult to test is usually a sign of inconvenient APIs and modules. For instance, the hiding of elements happens in multiple levels - the front-end needs a test to make sure the right intermediate representation is being generated. The backend, in turn, needs to be tested to make sure the intermediate representation with a hidden element generates the proper linker information and the linker itself needs a test to make sure the correctly annotated object code results in the correct artefact lacking external information about the hidden symbol. Testing end-to-end seems very laborious and error prone. Root-cause-analysis should have pinpointed the place the issue originates and one or more possible paths where it propagates downstream to inform future tests.

It also disturbs me that the author mentioned the order at which sources are compiled to matter in the final result. It should never matter.

When we build software we should always make it in such way it’s trivial to write tests for it. If writing a test is easy, it indicates using the tool you wrote is also easy.