1 files changed, 112 insertions, 0 deletions
diff --git a/scripts/tests/install-lang-collision.bats b/scripts/tests/install-lang-collision.bats
new file mode 100644
index 0000000..36abb5b
--- /dev/null
+++ b/scripts/tests/install-lang-collision.bats
@@ -0,0 +1,112 @@
+#!/usr/bin/env bats
+# Tests for install-lang's cross-bundle collision guard.
+#
+# Several bundles ship files at the same path. gitignore-add.txt merges
+# (appended, deduped) and CLAUDE.md is seed-only, so both compose across
+# bundles. Three do not:
+#
+#   claude/settings.json   elisp, bash, go   — cp -rT, silently overwritten
+#   githooks/pre-commit    elisp, bash, go   — cp -rT, silently overwritten
+#   coverage-makefile.txt  4 bundles         — [skip]ped, fragment dropped
+#
+# Installing a second bundle used to replace the first's settings.json and
+# pre-commit while printing [ok], so a project could lose its paren check or
+# secret scan and read the output as success. The guard refuses instead, naming
+# what would be replaced. FORCE=1 still overrides.
+
+INSTALL="${BATS_TEST_DIRNAME}/../install-lang.sh"
+
+setup() {
+  PROJ="$(mktemp -d)"
+  git init -q "$PROJ"
+}
+
+teardown() {
+  [ -n "${PROJ:-}" ] && rm -rf "$PROJ"
+}
+
+# ---- Normal: single-bundle installs are unaffected ----
+
+@test "install-lang: a fresh single-bundle install succeeds" {
+  run bash "$INSTALL" elisp "$PROJ"
+  [ "$status" -eq 0 ]
+  [ -f "$PROJ/.claude/settings.json" ]
+  grep -q 'validate-el.sh' "$PROJ/.claude/settings.json"
+}
+
+@test "install-lang: reinstalling the SAME bundle is idempotent, not a collision" {
+  bash "$INSTALL" elisp "$PROJ"
+  run bash "$INSTALL" elisp "$PROJ"
+  [ "$status" -eq 0 ]
+  [[ "$output" != *"collision"* ]]
+  grep -q 'validate-el.sh' "$PROJ/.claude/settings.json"
+}
+
+# ---- The guard: a second, different bundle must not silently replace ----
+
+@test "install-lang: a second bundle sharing settings.json and githooks is refused" {
+  bash "$INSTALL" elisp "$PROJ"
+  run bash "$INSTALL" bash "$PROJ"
+  [ "$status" -ne 0 ] || { echo "second bundle installed without refusal"; return 1; }
+  [[ "$output" == *"elisp"* ]] || { echo "refusal does not name the existing bundle"; return 1; }
+}
+
+@test "install-lang: the refusal names each file that would be replaced" {
+  bash "$INSTALL" elisp "$PROJ"
+  run bash "$INSTALL" bash "$PROJ"
+  [[ "$output" == *"settings.json"* ]] || { echo "refusal omits settings.json"; return 1; }
+  [[ "$output" == *"pre-commit"* ]] || { echo "refusal omits githooks/pre-commit"; return 1; }
+}
+
+@test "install-lang: a refused install leaves the first bundle intact" {
+  bash "$INSTALL" elisp "$PROJ"
+  bash "$INSTALL" bash "$PROJ" || true
+  grep -q 'validate-el.sh' "$PROJ/.claude/settings.json" \
+    || { echo "elisp settings.json was replaced despite refusal"; return 1; }
+  grep -q 'check-parens' "$PROJ/githooks/pre-commit" \
+    || { echo "elisp pre-commit was replaced despite refusal"; return 1; }
+}
+
+@test "install-lang: bundles colliding only on coverage-makefile.txt are refused too" {
+  # python and typescript ship no settings.json or githooks, but both ship a
+  # coverage fragment. The second one's used to be silently dropped.
+  bash "$INSTALL" python "$PROJ"
+  run bash "$INSTALL" typescript "$PROJ"
+  [ "$status" -ne 0 ] || { echo "typescript installed over python's coverage fragment"; return 1; }
+  [[ "$output" == *"coverage-makefile.txt"* ]]
+}
+
+@test "install-lang: two bundles that share no overwritten file install together" {
+  # bash ships settings.json + githooks and no coverage fragment; python ships
+  # only the coverage fragment. Nothing overlaps, so the guard must stay out of
+  # the way. This is the path where a false refusal would be easiest to
+  # introduce: the bundle IS detected, and only the empty file-list stops it.
+  bash "$INSTALL" bash "$PROJ"
+  run bash "$INSTALL" python "$PROJ"
+  [ "$status" -eq 0 ] || { echo "guard falsely refused a non-colliding pair: $output"; return 1; }
+  [ -f "$PROJ/coverage-makefile.txt" ] || { echo "python's coverage fragment did not land"; return 1; }
+  # bash's config survives untouched.
+  grep -q 'validate-bash.sh' "$PROJ/.claude/settings.json"
+  [ -f "$PROJ/.claude/rules/bash.md" ] && [ -f "$PROJ/.claude/rules/python-testing.md" ]
+}
+
+# ---- The escape hatch ----
+
+@test "install-lang: FORCE=1 overrides the collision guard" {
+  bash "$INSTALL" elisp "$PROJ"
+  run bash "$INSTALL" bash "$PROJ" 1
+  [ "$status" -eq 0 ] || { echo "FORCE=1 did not override: $output"; return 1; }
+  grep -q 'validate-bash.sh' "$PROJ/.claude/settings.json"
+}
+
+@test "install-lang: the refusal points at FORCE=1 and warns it re-seeds CLAUDE.md" {
+  bash "$INSTALL" elisp "$PROJ"
+  run bash "$INSTALL" bash "$PROJ"
+  # Assert the refusal fired first: the pre-existing "[skip] CLAUDE.md already
+  # exists (use FORCE=1 to overwrite)" line mentions both strings on its own, so
+  # without this the test passes against an unguarded install.
+  [ "$status" -ne 0 ] || { echo "no refusal fired"; return 1; }
+  refusal="$(printf '%s\n' "$output" | grep -v '^  \[skip\]')"
+  [[ "$refusal" == *"FORCE=1"* ]] || { echo "refusal does not name the override"; return 1; }
+  [[ "$refusal" == *"CLAUDE.md"* ]] || { echo "refusal does not warn about the CLAUDE.md re-seed"; return 1; }
+}