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LGTM, but agree with expect_death if able.

I'll give that another try today.

Yea looks like EXPECT_DEATH is unreliable in processes with more than one thread:

[ RUN      ] ValidationTest.IsFatal

[WARNING] ../../flutter/third_party/googletest/googletest/src/gtest-death-test.cc:1102:: Death tests use fork(), which is unsafe particularly in a threaded context. For this test, Google Test detected 6 threads. See https://github.com/google/googletest/blob/main/docs/advanced.md#death-tests-and-threads for more explanation and suggested solutions, especially if this is the last message you see before your test times out.
[FATAL:flutter/impeller/base/validation.cc(57)] Break on 'ImpellerValidationBreak' to inspect point of failure: 
Abort trap: 6

I looked to see if I could make sure the test happens first, presumably before the other threads are spawned, and it doesn't look like there is a way to make that the case reliably with googletest.