Very advanced type system which allows to move a lot of program correctness to typing system. So basically if your program compiles, it probably works.
It's also has GC which makes it better suited for most programs, compared to Rust with its manual memory management.
I hear this about both Haskell and Rust, and yet, when I tried both in the former I wrote a useless program because I didn't handle state (and yet passed all tests!) while in the latter I immediately wrote a deadlock.
Because it is also possible to write tests that don't adequately capture real-life requirements.
It was an MQTT server, and the tests basically went "if we have these subscriptions, then...", but no subscriptions ever got actually stored by the server.
I prefer the slogan without "probably", "If it compiles it works", because then at least it's clear it's a slogan and not a formal claim. Everyone knows that if you write
multiply x y = x + y
then it will compile but not work, so they don't take it literally. But it is a pithy statement of the lived experience of many users of strongly typed programming, which is more accurately described by something like "if it compiles then it will probably do something at least basically sensible and often be pretty close to what you actually wanted".
