> You should have test coverage, type checking, and integration tests that catch the edge cases automatically.

You should assume that if you are going to cover edge cases your tests will be tens to hundredths times as big as the code tested. It is the case for several database engines (MariaDB has 24M of C++ in sql directory and 288M of tests in mysql-test directory), it was the case when I developed VHDL/Verilog simulator. And not everything can be covered with type checking, many things, but not all.

AMD's FPU had hundredths of millions test cases for its' FPU and formal modeling caught several errors [1].

[1] https://www.cs.utexas.edu/~moore/acl2/v6-2/INTERESTING-APPLI...

SQLite used to have 1100 LOC of tests per one LOC of C code, now the multiplier is smaller, but still is big.