Bats
Bats is one of the most established testing frameworks for Bash, with TAP-compatible output and a compact syntax that fits shell-first projects well.
Usage
Write tests into *.bats files like:
#!/usr/bin/env bats
@test "addition using bc" {
result="$(echo 2+2 | bc)"
[ "$result" -eq 4 ]
}
Then run the test:
$ bats test.bats
✓ addition using bc
1 test, 0 failures