cargo test --help says:

    --example NAME ...           Check that the specified examples compile
    --examples                   Check that all examples compile

but what actually happens when you run cargo test --examples is that the examples are compiled and tested just like any other test, and the binary written to target/debug/examples/$NAME is a test-runner rather than the actual example binary.

This may seem harmless but it causes a surprising difference in behaviour when e.g. running cargo test && target/debug/examples/$NAME vs cargo test --examples && target/debug/examples/$NAME.

Uncovered by a proposed addition to #5146.