Why is everyone in this thread forgetting what tests actually do?
Tests force you to write better code. Code that is easier to change. Code that is more robust.
You don't need 100% coverage or perfect tests to gain this benefit.
A good test suite enables you to make large refractors safely and quickly.
The most scary refractors I've ever had to do are ones that involve large changes to code that has no tests.
Often those refractors that allow company level pivots require adding huge amounts of tests to a legacy code base before I can even get started.
Adding tests to code that has none is the worst. The code is coupled all over the shop and requires 100 times more mocking and stubbing to get under tests when you add this stuff retroactively.
Tests speed up development velocity and improve your codebase.
Just don't get stupid about it and you won't negatively impact startup performance.