The bats test for migration idempotency invoked the install binary directly via sudo, which kept hitting fresh missing env vars on each iteration (DOKKU_LIB_ROOT, then PLUGIN_PATH, etc). The dokku launcher script exports a chain of vars that the install path reads via common.MustGetEnv, and mirroring that chain in a bats test is fragile. Migration is pure file IO plus a property marker - perfect for a Go unit test that isolates itself with t.TempDir and t.Setenv. The new test covers parsing comments and blank lines, the marker-based no-op on re-run, and the rule that a manually re-created legacy file is left untouched after the marker is set.
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