test(watch): unit cover watch_get_checksum polling helper

src/main.sh

@@ -543,14 +543,14 @@ function bashunit::main::watch_get_checksum() {
     if [ -d "$file" ]; then
       local found
       found=$(find "$file" -name '*.sh' -type f \
-        -exec stat -f '%m %N' {} + 2>/dev/null ||
+        -exec stat -c '%Y %n' {} + 2>/dev/null ||
         find "$file" -name '*.sh' -type f \
-          -exec stat -c '%Y %n' {} + 2>/dev/null) || true
+          -exec stat -f '%m %N' {} + 2>/dev/null) || true
       checksum="${checksum}${found}"
     elif [ -f "$file" ]; then
       local mtime
-      mtime=$(stat -f '%m' "$file" 2>/dev/null ||
-        stat -c '%Y' "$file" 2>/dev/null) || true
+      mtime=$(stat -c '%Y' "$file" 2>/dev/null ||
+        stat -f '%m' "$file" 2>/dev/null) || true
       checksum="${checksum}${mtime} ${file}"
     fi
   done

tests/unit/watch_checksum_test.sh

@@ -0,0 +1,82 @@
+#!/usr/bin/env bash
+
+# shellcheck disable=SC2329 # Test functions are invoked indirectly by bashunit
+
+############################
+# bashunit::main::watch_get_checksum
+############################
+
+function test_checksum_is_stable_for_unchanged_paths() {
+  local dir
+  dir=$(bashunit::temp_dir watch_stable)
+  : >"$dir/foo.sh"
+
+  local first second
+  first=$(bashunit::main::watch_get_checksum "$dir")
+  second=$(bashunit::main::watch_get_checksum "$dir")
+
+  assert_equals "$first" "$second"
+}
+
+function test_checksum_changes_when_file_mtime_changes() {
+  local dir
+  dir=$(bashunit::temp_dir watch_change)
+  local file="$dir/foo.sh"
+  : >"$file"
+  touch -t 202001010000 "$file"
+
+  local before after
+  before=$(bashunit::main::watch_get_checksum "$dir")
+  touch -t 202501010000 "$file"
+  after=$(bashunit::main::watch_get_checksum "$dir")
+
+  assert_not_equals "$before" "$after"
+}
+
+function test_checksum_differs_when_new_file_appears() {
+  local dir
+  dir=$(bashunit::temp_dir watch_new_file)
+  : >"$dir/a.sh"
+
+  local before after
+  before=$(bashunit::main::watch_get_checksum "$dir")
+  : >"$dir/b.sh"
+  after=$(bashunit::main::watch_get_checksum "$dir")
+
+  assert_not_equals "$before" "$after"
+}
+
+function test_checksum_ignores_non_sh_files() {
+  local dir
+  dir=$(bashunit::temp_dir watch_non_sh)
+  : >"$dir/keep.sh"
+
+  local before after
+  before=$(bashunit::main::watch_get_checksum "$dir")
+  : >"$dir/ignored.txt"
+  : >"$dir/ignored.md"
+  after=$(bashunit::main::watch_get_checksum "$dir")
+
+  assert_equals "$before" "$after"
+}
+
+function test_checksum_handles_single_file_path() {
+  local dir
+  dir=$(bashunit::temp_dir watch_file)
+  local file="$dir/single.sh"
+  : >"$file"
+  touch -t 202001010000 "$file"
+
+  local before after
+  before=$(bashunit::main::watch_get_checksum "$file")
+  touch -t 202501010000 "$file"
+  after=$(bashunit::main::watch_get_checksum "$file")
+
+  assert_not_equals "$before" "$after"
+}
+
+function test_checksum_is_empty_for_missing_path() {
+  local missing="/nonexistent/path/$$/xyz"
+
+  assert_empty "$(bashunit::main::watch_get_checksum "$missing")"
+}