The Greek doesn't have "test and approve" (NIV) or "by testing you may discern" (ESV) - it has one word, "prove" (NASB). The word does have both the sense of testing and approving, but the NIV makes it sounds like you do two things (which the verse doesn't say), and the ESV makes it sounds like you do one thing by doing another thing (which the verse doesn't say). Those are *interpretations* that belong in footnotes, not the translation.

Romans 12:2