One solid practice to have while coding is to fix a bug and at the same time write a unit test that would have uncovered it. It is a sign of solid experience in software engineering. The direct benefits are to avoid regressions for this bug, to ensure the fix is correct and to increase code coverage and the reliability of the test suite.
Usually I write the unit test first, to make sure it actually finds the bug, then fix it. (Which is probably how you mean this, but clarity is good.)
Red-to-green feels so nice!