Interpreter and runtime
Also called Runtime, Node.js
An interpreter runs source code directly, working through it as it goes, so many problems only appear when reached. A runtime is what a program needs around it while running. Python, Node.js and Bun are examples. The line with compilers is blurry.
With no compile step, code that never ran is code nothing has checked. An agent can show you a working demo while a misspelt name waits on a path through the code it never took. So running the script once proves that one path. Tests have to go down the others.
Say it to your agent
“This is Python, so a bad name in that error branch only fails when the branch runs. Add a test that forces the payment to fail and goes through that branch, and show me it passing.”