[Tests] GetProcessTmpDir_ChildProcess_ReadsTmpdir fails with Assert.Equal() Failure

[mdh1418]

The GetProcessTmpDir_ChildProcess_ReadsTmpdir unit test (introduced in #5735) fails intermittently on the Ubuntu 22.04 x64 CI leg. The test spawns a child process with TMPDIR=/custom/tmp/test via ProcessStartInfo.Environment, then verifies that GetProcessTmpDir reads
the custom value from /proc/{pid}/environ.

Failure

Assert.Equal() Failure: Strings differ ↓ (pos 1) Expected: "/custom/tmp/test" Actual: "/tmp/" ↑ (pos 1)

The environ file was successfully read (environReadable = true), but the parsed TMPDIR was /tmp/ (the Path.GetTempPath() fallback) instead of the custom value set via ProcessStartInfo.Environment.

Possible Causes

• Race condition: The child process's /proc/{pid}/environ may not reflect the overridden environment if read before execve completes
• Empty environ: Some CI configurations may return readable but empty /proc/{pid}/environ
• Environment propagation: ProcessStartInfo.Environment override may not propagate in certain CI environments

[steveisok]

Additional data from rolling CI analysis:

This also reproduces on Alpine 3.19 x64, not just Ubuntu 22.04. Same exact failure — Assert.Equal expecting /custom/tmp/test, getting /tmp/. Seen in:

• Build 1332642 (Mar 12, Alpine3_19_x64_Release)
• Build 1322735 (Mar 5, Ubuntu_22_04_x64_Release)

Possible race condition: The test has no delay between Process.Start(psi) and calling GetProcessTmpDir(child.Id, ...). On Linux, /proc/{pid}/environ may not immediately reflect the child's environment if the read happens between fork() and exec(). A short polling loop or delay after start may help.

Note: the #5751 diagnostics have not yet triggered on these legs because the most recent builds (1332940) are dominated by the SOS DAC loading failure (#5757), which masks this test.

[hoyosjs]

Extended error message:

Expected '/custom/tmp/test' but got '/tmp/'.
Child PID: 16253,
child exited: False,
environ path: /proc/16253/environ,
environ permissions: UserRead,
parent TMPDIR: '(not set)',
psi.Environment TMPDIR: '/custom/tmp/test',
current user: cloudtest_azpcontainer,
environ size: 0 bytes,
env var count: 0,
TMPDIR entry: '(not found)',
first 200 chars of environ: ''