As always, "it depends." Testing is usually about larger teams, cost of failure, and sleeping better at night during refactors.

If the project is small, fits in one skull, and not critical enough to be maintained/redesigned for years on end tests buy you less.

Also, technology can prevent some classes of problems, such as type checkers, linters, etc. One hopes you are at least using these.

#1 gives the impression the author is using a dynamic "scripting" language, which may require a higher ratio of tests per line as a project matures.