I've noticed on my system I get lots of temp files in /tmp/ (I'm on Ubuntu 15.10). I've tested (I just run npm test, which I know makes at least one call to exec() per test) under the following versions of node:

• v0.10: everything gets cleaned up
• v0.11, v0.12, v4, v5: npm test leaves 1 code file, 2 script files, 2 stderr files, and 2 stdout files

v0.11 is when execSync() got introduced, so this could be related.