I'll agree that if you have an important invariant then it's nice if the compiler can check it. But the question to ask is: where did these constraints come from? How do you know they're true? What if they change?
If they're business requirements: can you undo them if the business changes? If they're environmental constraints: do you really know mobile phones or browsers or the server OS that well, and what do you do when a new version of the environment comes out and invalidates your assumptions?
Generally speaking, it seems better to take our inspiration from scientists doing empirical work, rather than from mathematicians. Use tests to figure out how the code you depend on really behaves, not how you wish it would behave.
If they're business requirements: can you undo them if the business changes? If they're environmental constraints: do you really know mobile phones or browsers or the server OS that well, and what do you do when a new version of the environment comes out and invalidates your assumptions?
Generally speaking, it seems better to take our inspiration from scientists doing empirical work, rather than from mathematicians. Use tests to figure out how the code you depend on really behaves, not how you wish it would behave.