diff --git a/test/smoke-test.sh b/test/smoke-test.sh
index b18ec85..8779cc9 100755
--- a/test/smoke-test.sh
+++ b/test/smoke-test.sh
@@ -70,17 +70,6 @@ for skill in $SKILLS; do
   check "$skill has SKILL.md.tmpl" "[ -f '$IDSTACK_DIR/skills/$skill/SKILL.md.tmpl' ]"
 done
 
-# Slugify behavior — pinned cases protect the slug derivation rule that the manifest
-# schema and every skill's report-write block depend on.
-check "idstack-slugify: 'Introduction to Biology 101' → introduction-to-biology-101" \
-  "[ \"\$('$IDSTACK_DIR/bin/idstack-slugify' 'Introduction to Biology 101')\" = 'introduction-to-biology-101' ]"
-check "idstack-slugify: empty input → untitled-course" \
-  "[ \"\$('$IDSTACK_DIR/bin/idstack-slugify' '')\" = 'untitled-course' ]"
-check "idstack-slugify: '!!!' → untitled-course" \
-  "[ \"\$('$IDSTACK_DIR/bin/idstack-slugify' '!!!')\" = 'untitled-course' ]"
-check "idstack-slugify: unicode ASCII-folds — 'Géographie I' → geographie-i" \
-  "[ \"\$('$IDSTACK_DIR/bin/idstack-slugify' 'Géographie I')\" = 'geographie-i' ]"
-
 # Skills that write per-skill HTML reports must reference the new export folder pattern
 # and use the slugify helper (not the legacy .idstack/reports/<skill>.md path).
 REPORT_PRODUCING_SKILLS="needs-analysis learning-objectives assessment-design course-builder course-quality-review course-import course-export accessibility-review red-team"
@@ -147,6 +136,11 @@ if [ -x "$IDSTACK_DIR/test/test-version-classifier.sh" ]; then
   check "version-classifier unit tests pass" "'$IDSTACK_DIR/test/test-version-classifier.sh'"
 fi
 
+# Slugify (derives filesystem-safe slug from a string)
+if [ -x "$IDSTACK_DIR/test/test-slugify.sh" ]; then
+  check "slugify unit tests pass" "'$IDSTACK_DIR/test/test-slugify.sh'"
+fi
+
 # Check generated files have auto-generated header
 for skill in $SKILLS; do
   check "$skill SKILL.md has auto-generated header" "grep -q 'AUTO-GENERATED from SKILL.md.tmpl' '$IDSTACK_DIR/skills/$skill/SKILL.md'"
diff --git a/test/test-slugify.sh b/test/test-slugify.sh
new file mode 100755
index 0000000..ba38927
--- /dev/null
+++ b/test/test-slugify.sh
@@ -0,0 +1,104 @@
+#!/usr/bin/env bash
+# Unit tests for bin/idstack-slugify.
+# Run from the repo root (or sourced by smoke-test.sh).
+
+set -e
+
+PASS=0
+FAIL=0
+TOTAL=0
+
+REPO_ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+SLUGIFY="$REPO_ROOT/bin/idstack-slugify"
+
+assert() {
+  TOTAL=$((TOTAL + 1))
+  local description="$1"
+  local command="$2"
+  local expected="$3"
+
+  local got
+  # Run the command, safely capturing output.
+  if got=$(eval "$command" 2>/dev/null); then
+    if [ "$got" = "$expected" ]; then
+      PASS=$((PASS + 1))
+      echo "  PASS: $description -> $got"
+    else
+      FAIL=$((FAIL + 1))
+      echo "  FAIL: $description -> $got (expected: $expected)"
+    fi
+  else
+    FAIL=$((FAIL + 1))
+    echo "  FAIL: $description (command failed unexpectedly)"
+  fi
+}
+
+assert_exit_code() {
+  TOTAL=$((TOTAL + 1))
+  local description="$1"
+  local command="$2"
+  local expected_code="$3"
+
+  set +e
+  eval "$command" >/dev/null 2>&1
+  local code=$?
+  set -e
+
+  if [ "$code" -eq "$expected_code" ]; then
+    PASS=$((PASS + 1))
+    echo "  PASS: $description -> exit code $code"
+  else
+    FAIL=$((FAIL + 1))
+    echo "  FAIL: $description -> exit code $code (expected: $expected_code)"
+  fi
+}
+
+
+if [ ! -x "$SLUGIFY" ]; then
+  echo "test-slugify: $SLUGIFY missing or not executable"
+  exit 1
+fi
+
+echo "test-slugify"
+echo ""
+
+# --- Happy path: standard strings ---
+assert "standard string" "'$SLUGIFY' 'Introduction to Biology 101'" "introduction-to-biology-101"
+assert "lowercase stays lowercase" "'$SLUGIFY' 'hello world'" "hello-world"
+assert "uppercase becomes lowercase" "'$SLUGIFY' 'HELLO WORLD'" "hello-world"
+
+# --- Edge cases: special characters and hyphens ---
+assert "multiple spaces become single hyphen" "'$SLUGIFY' 'hello   world'" "hello-world"
+assert "special characters become hyphens" "'$SLUGIFY' 'hello!@#world'" "hello-world"
+assert "leading hyphens are stripped" "'$SLUGIFY' '---hello'" "hello"
+assert "trailing hyphens are stripped" "'$SLUGIFY' 'world---'" "world"
+assert "mixed hyphens and spaces" "'$SLUGIFY' '  -hello-  world- '" "hello-world"
+assert "all special characters" "'$SLUGIFY' '!@#$%^&*()'" "untitled-course"
+assert "only hyphens" "'$SLUGIFY' '---'" "untitled-course"
+assert "only spaces" "'$SLUGIFY' '   '" "untitled-course"
+
+# --- Edge case: empty input ---
+assert "empty string" "'$SLUGIFY' ''" "untitled-course"
+
+# --- Unicode and accents (NFKD folding) ---
+assert "unicode folding (é, I)" "'$SLUGIFY' 'Géographie I'" "geographie-i"
+assert "unicode characters" "'$SLUGIFY' 'Über den Wolken'" "uber-den-wolken"
+assert "non-ascii stripped" "'$SLUGIFY' 'Hello 🌍 World'" "hello-world"
+
+# --- Input methods ---
+assert "stdin implicitly" "echo 'Pipe Test' | '$SLUGIFY'" "pipe-test"
+assert "stdin explicitly with hyphen" "echo 'Explicit Pipe' | '$SLUGIFY' -" "explicit-pipe"
+
+# --- Error cases ---
+# Test exit code 3 when no argument and no stdin
+# The tool checks [ -t 0 ] to detect if it's connected to a terminal.
+# We simulate a terminal using python's pty module.
+if command -v python3 >/dev/null 2>&1; then
+  assert_exit_code "no input given (exit 3)" "python3 -c 'import sys, os, pty, subprocess; pid, fd = pty.fork(); sys.exit(subprocess.call([\"$SLUGIFY\"])) if pid == 0 else sys.exit(os.waitstatus_to_exitcode(os.waitpid(pid, 0)[1]))'" 3
+else
+  echo "  SKIP: no input given (exit 3) — python3 required for pty simulation"
+fi
+
+echo ""
+echo "slugify: $PASS/$TOTAL passed, $FAIL failed"
+[ "$FAIL" -eq 0 ] && exit 0 || exit 1