For me at least, designing a test will usually let me discover problems with my code which may otherwise gone unnoticed.

Leaving the tests there once written to help us in future refactoring costs nothing.

Granted, in some languages tests are more complicated to write compared to others. In PHP it’s a nightmare, in Rust it’s so easy it’s hard to avoid doing.

I hear what you are saying though, sometimes writing tests consume more time then is necessary.