[CSM-540]: Add unit tests for component

[oykukurtgoz]

Closes CSM-540.

Adds unit tests for main.rb.

The whole PR is 462 added lines and 12 deleted ones; main.rb accounts for 17 added and 12 deleted. Nothing in the install logic was moved or reworded — the version selection, the Selected node version is … line, the n / sudo n commands and the Unexpected OS abort are byte-for-byte what they were.

Changes to main.rb

Two, both driven by the issue's prerequisite refactor.

Top-level side effects are guarded. The version-selection lines that used to sit between get_version and run_command, and the OS branch at the bottom of the file, now sit together inside a single if __FILE__ == $PROGRAM_NAME ... end block, in their original order. Appcircle runs the step with ruby main.rb, so the guard is true there and the body executes exactly as before. require-ing the file only defines env_has_key, get_version and run_command.

os is loaded inside begin/rescue LoadError. It is a gem rather than stdlib, so a bare test environment may not have it. When it is installed nothing changes; when it is not, the file still loads and the tests supply a stub OS module. open3 is stdlib and is left as a plain require.

No nil-unsafe access surfaced in the real flow, so no explicit raise was added. env_has_key(nil) and run_command(nil) are never reached by the script; the tests pin their current TypeError behaviour rather than change it.

Tests (test/test_main.rb)

Self-executing, 28 examples, no Gemfile / Bundler — rspec gem + Ruby stdlib only.

ruby test/test_main.rb

main.rb exposes three functions plus the script as a whole, and the tests cover all four surfaces:

• env_has_key, in-process — returns the value when set, returns nil for a missing key, an empty string and an empty key name, raises TypeError for a nil key.
• get_version, in-process — returns the config version when set, falls back to the component version when the config version is nil, returns an empty config version as-is, returns nil when both are nil.
• run_command, in-process — Open3.popen3 is stubbed with StringIO streams and a fake wait_thr, so no real command runs. Happy path, the echoed @@[command] line and forwarded stdout lines, the exact command string handed to popen3, the failure branch (SystemExit status 1 carrying the child's stderr, and an empty stderr), plus nil and empty commands. Two further cases run a real echo and a real sh -c "exit 1" the same way the reference PRs do.
• The script as a whole, in-process — $PROGRAM_NAME is pointed at main.rb and the file is load-ed with Open3.popen3 stubbed and OS.linux? / OS.mac? stubbed per case. This asserts the composed command string end to end: n lts by default, n 18 from AC_SELECTED_NODE_VERSION, AC_NODE_JS_VERSION overriding it, empty values of either being ignored, sudo n … on macOS, Unexpected OS abort with no command on any other OS, and the stderr of a failing install being propagated through abort.
• Loading as a library — require-ing main.rb in a fresh process through Open3.capture3 exits 0 and prints no Selected node version line.

The script declares no required environment variables, so there are no missing-and-empty validation subprocess cases; the empty-value behaviour of the two optional variables is covered by the in-process step cases above.

No real toolchain (n, sudo), network, or filesystem writes.

Coverage

✔  All 28 tests passed
main.rb  100.0%  (29/29 lines)

One detail worth knowing: Ruby's Coverage resets a file's counters every time that file is load-ed again. Since the step-level cases load main.rb once each, the test file takes a Coverage.peek_result snapshot before every load and sums the snapshots into the final report. Without that the report would only reflect the last load.

Docs

README.md gains a ## Running tests section.

🤖 Generated with Claude Code

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