fix: tests write temporary files under tmp/

264 TemporaryDirectory() and mkdtemp() calls without dir= wrote to the
/tmp tmpfs, and a full tmpfs failed modules no change touched. The test
package now points tempfile and TMPDIR at tmp/tests, and sets
GIT_CEILING_DIRECTORIES there so git run in a scratch directory does
not find the checkout above it. The package test asserts both.

tests/__init__.py

@@ -13,6 +13,7 @@ temporary directory instead of naming the missing parent.
 from __future__ import annotations
 
 import os
+import tempfile
 from pathlib import Path
 
 os.environ.setdefault("RETROBIOS_OFFLINE", "1")
@@ -22,9 +23,16 @@ os.environ.setdefault(
     str(Path(__file__).resolve().parent.parent / "tmp" / "tests" / "probe.lock"),
 )
 
-(Path(__file__).resolve().parent.parent / "tmp" / "tests").mkdir(
-    parents=True, exist_ok=True
-)
+_SCRATCH = Path(__file__).resolve().parent.parent / "tmp" / "tests"
+_SCRATCH.mkdir(parents=True, exist_ok=True)
+# A TemporaryDirectory() without dir= landed in /tmp, a 4 GB tmpfs here: once
+# another run filled it, modules unrelated to any change failed with ENOSPC.
+# The default is the repository's tmp/, for this process and its children.
+os.environ["TMPDIR"] = str(_SCRATCH)
+tempfile.tempdir = str(_SCRATCH)
+# A scratch directory is not part of this checkout: git run inside one must
+# not walk up to the repository, as it could not from /tmp.
+os.environ["GIT_CEILING_DIRECTORIES"] = str(_SCRATCH)
 # The installer's cache (the games index, what reading a card found) is the
 # suite's own: a run never reads nor fills the one of the person running it.
 os.environ.setdefault(

tests/test_audit_regressions.py

@@ -206,11 +206,16 @@ class AModuleRunAloneHasItsScratchDirectory(unittest.TestCase):
             )
             proc = subprocess.run(
                 [sys.executable, "-I", "-c",
-                 "import sys; sys.path.insert(0, '.'); import tests"],
+                 "import sys; sys.path.insert(0, '.'); import tests, tempfile, os;"
+                 " print(tempfile.gettempdir()); print(os.environ['TMPDIR'])"],
                 cwd=clone, capture_output=True, text=True, timeout=60, check=False,
             )
             self.assertEqual(proc.returncode, 0, proc.stderr)
             self.assertTrue((clone / "tmp" / "tests").is_dir())
+            # 264 TemporaryDirectory() calls without dir= wrote to the /tmp
+            # tmpfs, and a full tmpfs failed modules no change touched.
+            scratch = str((clone / "tmp" / "tests").resolve())
+            self.assertEqual(proc.stdout.split(), [scratch, scratch])
 
 
 class ReleaseSigningRegressions(unittest.TestCase):

wiki/testing-guide.md

@@ -9,9 +9,11 @@ The tests hold what users and platforms rely on: a pack holds what its
 platform checks, the site states what the code does, the installer writes only
 where it should.
 
-No test needs network access. Most build synthetic fixtures under the
-repository's `tmp/`, and modules that read real artifacts skip when those are
-absent. The test runner prints the count.
+No test needs network access. Most build synthetic fixtures, and every
+temporary directory lands under the repository's `tmp/tests/`:
+`tests/__init__.py` points `tempfile` and `TMPDIR` there, never at the `/tmp`
+tmpfs. Modules that read real artifacts skip when those are absent. The test
+runner prints the count.
 
 ## Running tests