Write a Bats test

You want to test a shell function the way you test code in any other language, with named cases and a pass or fail result.

cat > test.bats <<'EOF'
@test "addition works" {
  result=$((2 + 3))
  [ "$result" -eq 5 ]
}

@test "grep finds a word" {
  echo "hello world" | grep -q world
}

@test "this one fails" {
  [ "$((2 + 2))" -eq 5 ]
}
EOF
bats test.bats
echo "exit: $?"

1..3
ok 1 addition works
ok 2 grep finds a word
not ok 3 this one fails
# (in test file test.bats, line 11)
#   `[ "$((2 + 2))" -eq 5 ]' failed
exit: 1

Each @test block becomes a shell function that runs with set -e in effect, so the first command that returns non-zero fails the test, which is why a bare [ ... ] is an assertion. Bats prints the TAP format, a plan line followed by an ok or not ok for each case, and for a failure it names the file, the line and the command that failed.

The exit status of bats is 1 when any test fails, so it works as a CI step. A command that fails inside an if or after || does not trip set -e, so write assertions as plain commands. The output here is from Bats 1.8.2, and the @test syntax needs the bats runner and is not valid Bash on its own.