Describe the bug
Running on Mac, BATS_TMPDIR uses the value of TMPDIR that has a trailing slash.

This results in BATS_TMPDIR having values like

/var/folders/5f/p33sf8dj1317jl051f62h09c0000gp/T//bats-run-6SF0zp/bats-test-tmp-0P8F

As per

If a test performs string replacements based on paths, the OS would remove those // while the BATS_TMPDIR will still hold them as a string. This results in test failures since 2 strings do not match.

I.e.

/var/folders/5f/p33sf8dj1317jl051f62h09c0000gp/T//bats-run-6SF0zp/bats-test-tmp-0P8F

and

/var/folders/5f/p33sf8dj1317jl051f62h09c0000gp/T/bats-run-6SF0zp/bats-test-tmp-0P8F

Similar problem exists for BATS_TEST_TMPDIR:

/var/folders/5f/p33sf8dj1317jl051f62h09c0000gp/T//bats-run-6SF0zp/test//1

Note: this started to appear after upgrade from 1.3.0 to 1.7.0

I have a very extensive test suite that uses helpers (and tests them) + a lot of actual tests running locally and in CI (and failing now).

To Reproduce
Steps to reproduce the behavior:

1. Run on MacOS echo $BATS_TMPDIR within a test and assert that output contains //

Expected behavior
No // in the path.

Environment (please complete the following information):

• Bats Version: 1.7
• OS: MacOS (local), Linux (CI)
• Bash version: GNU bash, version 5.1.4(1)-release (x86_64-apple-darwin20.2.0)

Additional context

Others have experienced this as well: golang/go#21318

Some additional info: How does Linux handle multiple consecutive path separators (/home////username///file)?