Test fails but all testcases succeed - what's happening?

I'm having an issue with a failing test. The testcases for that test all succeed, but the test itself fails with some error output (generated by clap).

Here is the appropriate travis job. The error can be reproduced with executing

cargo test --manifest-path bin/core/imag-link/Cargo.toml tests::test_linking_links

in the repository.

Can someone figure out what is happening? I cannot, I'm completely confused.

Error output for the lazy:

     Running target/debug/deps/imag_link-ac3048304d1b8c93

running 2 tests
test tests::test_linking_links ... ok
error: The following required arguments were not provided:

    imag-link <ENTRY> <ENTRIES>... --rtp <runtimepath> --verbose <LOGLEVEL>

The error isn't coming from cargo. It's most likely a side-effect of one of the tests, which runs an executable. It's either intended (the test expects the executable to fail when run with no arguments), or some test isn't checking that failure.