A note for people with the same error message.
A test case was terminated with the above error message.
The analysis showed that the wrong data type was used in a for loop.
Wrong
for (size_t line = 1; line >= 0; line--)
Correct
for (int line = 1; line >= 0; line--)
The test case was terminated correctly with the correct data type.
Your post lacks of context.
An unsigned data type can never be less than zero.
That is fundamental and is not related to Gtest and PlatformIO.
That’s clear, I just wanted to point out that a programming error can lead to the above error code. There are various hints in the community for possible problems, but none of them involve programming errors.