chore(common): add unit tests for detect

Author: nickchecan

Makefile

@@ -6,12 +6,16 @@ ROOT_DIR := $(CURDIR)
 BUILDPACK_DIR := $(ROOT_DIR)
 PYTHON_BIN ?= python3
 
-.PHONY: test-buildpack clean-test-buildpack smoke-test start-local
+.PHONY: test-buildpack clean-test-buildpack test-detect smoke-test start-local
 
 # Reset the temporary staging directories used for local buildpack testing.
 clean-test-buildpack:
 	rm -rf $(BUILD_DIR) $(CACHE_DIR) $(ENV_DIR)
 
+# Run unit tests for the detect script without requiring external test tooling.
+test-detect:
+	@bash ./test/unit/detect_test.sh
+
 # Run the sample app through detect, compile, and release using the same
 # temporary directories each time so local testing is repeatable.
 test-buildpack: clean-test-buildpack

test/unit/detect_test.sh

@@ -0,0 +1,117 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
+DETECT_SCRIPT="$ROOT_DIR/bin/detect"
+TMP_DIR="$(mktemp -d /tmp/detect-test.XXXXXX)"
+
+cleanup() {
+  rm -rf "$TMP_DIR"
+}
+
+trap cleanup EXIT
+
+assert_exit_code() {
+  local actual="$1"
+  local expected="$2"
+  local message="$3"
+
+  if [ "$actual" -ne "$expected" ]; then
+    echo "FAIL: $message"
+    echo "Expected exit code: $expected"
+    echo "Actual exit code: $actual"
+    exit 1
+  fi
+}
+
+assert_output() {
+  local actual="$1"
+  local expected="$2"
+  local message="$3"
+
+  if [ "$actual" != "$expected" ]; then
+    echo "FAIL: $message"
+    echo "Expected output: $expected"
+    echo "Actual output: $actual"
+    exit 1
+  fi
+}
+
+run_detect() {
+  local app_dir="$1"
+  local output_file="$TMP_DIR/output.txt"
+
+  set +e
+  (
+    cd "$app_dir"
+    "$DETECT_SCRIPT"
+  ) >"$output_file" 2>&1
+  status=$?
+  set -e
+
+  output="$(cat "$output_file")"
+}
+
+test_detect_succeeds_when_pyproject_and_lockfile_exist() {
+  # Arrange
+  local app_dir="$TMP_DIR/success-case"
+  mkdir -p "$app_dir"
+  touch "$app_dir/pyproject.toml" "$app_dir/uv.lock"
+
+  # Act
+  run_detect "$app_dir"
+
+  # Assert
+  assert_exit_code "$status" 0 "detect should succeed when both uv files exist"
+  assert_output "$output" "python-uv" "detect should print the buildpack id when it succeeds"
+}
+
+test_detect_fails_when_lockfile_is_missing() {
+  # Arrange
+  local app_dir="$TMP_DIR/missing-lock"
+  mkdir -p "$app_dir"
+  touch "$app_dir/pyproject.toml"
+
+  # Act
+  run_detect "$app_dir"
+
+  # Assert
+  assert_exit_code "$status" 1 "detect should fail when uv.lock is missing"
+  assert_output "$output" "" "detect should not print anything when detection fails"
+}
+
+test_detect_fails_when_pyproject_is_missing() {
+  # Arrange
+  local app_dir="$TMP_DIR/missing-pyproject"
+  mkdir -p "$app_dir"
+  touch "$app_dir/uv.lock"
+
+  # Act
+  run_detect "$app_dir"
+
+  # Assert
+  assert_exit_code "$status" 1 "detect should fail when pyproject.toml is missing"
+  assert_output "$output" "" "detect should not print anything when detection fails"
+}
+
+test_detect_succeeds_when_extra_files_are_present() {
+  # Arrange
+  local app_dir="$TMP_DIR/extra-files"
+  mkdir -p "$app_dir"
+  touch "$app_dir/pyproject.toml" "$app_dir/uv.lock" "$app_dir/README.md"
+
+  # Act
+  run_detect "$app_dir"
+
+  # Assert
+  assert_exit_code "$status" 0 "detect should ignore unrelated files"
+  assert_output "$output" "python-uv" "detect should still identify a supported uv app"
+}
+
+test_detect_succeeds_when_pyproject_and_lockfile_exist
+test_detect_fails_when_lockfile_is_missing
+test_detect_fails_when_pyproject_is_missing
+test_detect_succeeds_when_extra_files_are_present
+
+echo "PASS: detect unit tests"