The lesson learned isn’t about code coverage or oaths tested. It’s to not blindly trust 3rd part anything, even “languages already have test with very good coverage” when the stakes are high.
If billions of dollars are riding on your code, you better be damn sure you trust everything it relies on.
Fun side note: every piece of internal code was always developed in parallel to the same spec by 3+ teams so they could cross validate. If all 3 functions don’t return the same value for the same input, every team gets to build it again until all implementations behave the exact same.
Certainly it's fun from the pure engineering perspective but I guess also somewhat tedious.
On the other hand, if a billion dollars depend on your code working or not, or in other cases human lives like in space rockets, you don't get a second chance. If you fuck up, lots of important things get flushed down the toilet, usually including your job.
So you have 3 teams do in parallel to be 99.999999999% certain that it'll work as advertised. It's also sorta why banks are slow to adopt new changes since they want to be sure that whatever is going on, it'll work and not flush down Grandma's rent.
If billions of dollars are riding on your code, you better be damn sure you trust everything it relies on.
Fun side note: every piece of internal code was always developed in parallel to the same spec by 3+ teams so they could cross validate. If all 3 functions don’t return the same value for the same input, every team gets to build it again until all implementations behave the exact same.
High reliability engineering sounds “fun”