make verify fails on stock macOS: "test_flags[@]: unbound variable" in hack/test.sh

[corioliskraft]

Description

make verify fails at the test target on a stock macOS machine. hack/test.sh expands an empty array under set -u, which older bash treats as an unbound variable. macOS ships bash 3.2.57 as /bin/bash, and #!/usr/bin/env bash resolves to it unless a newer bash is installed separately.

Steps to reproduce

1. On macOS with no third-party bash installed (/bin/bash --version reports 3.2.57(1)).
2. Clone the repository and run make verify in the repository root.

How to reproduce this behavior without the repository:

$ /bin/bash -c 'set -u; a=(); echo "${a[@]}"'
bash: a[@]: unbound variable

Actual behavior

verify-fmt, verify-modules, verify-generate and lint pass, then:

./hack/test.sh ./cmd/... ./pkg/...
> Unit Tests
./hack/test.sh: line 27: test_flags[@]: unbound variable
make: *** [test] Error 1

hack/test.sh sets nounset (line 4). Outside CI the else branch (lines 22-25) is taken, so test_flags stays empty, and line 27 expands it:

go test ${timeout_flag:+"$timeout_flag"} "$@" "${test_flags[@]}"

Prow is unaffected: there CI and ARTIFACTS are set, so the if branch appends two elements and test_flags is never empty.

Expected behavior

make verify runs the unit tests instead of aborting, on any platform where the documented prerequisites are met. Neither CONTRIBUTING.md nor docs/development.md states an OS or a minimum bash version.

Suggested fix: guard the expansion so it disappears when the array is empty:

go test ${timeout_flag:+"$timeout_flag"} "$@" ${test_flags[@]+"${test_flags[@]}"}

Verified on bash 3.2.57.

PR will follow.

Environment

• Kubernetes version: n/a, fails at build/verify time
• Version of the cloud-provider-stackit: main at commit 83f9aae

Additional information

• macOS 15.7.7, arm64
• /bin/bash 3.2.57(1)-release
• Contributors with Homebrew or MacPorts bash earlier on PATH get bash 5.x and do not hit this,
  which is likely why it went unnoticed.

/kind bug