diff --git a/shpy b/shpy
index bceaf4e..76c2d4a 100644
--- a/shpy
+++ b/shpy
@@ -29,7 +29,7 @@ createSpy() {
               echo "$OPTARG" > "$errors_dir/$error_num"
               error_num=$((error_num + 1))
               ;;
-            r) val="$val $OPTARG" ;;
+            r) val="${val:-} $OPTARG" ;;
             *) shpy_die "Error: Unknown option -$OPTARG" ;;
         esac
     done
@@ -37,7 +37,7 @@ createSpy() {
     shift $(( OPTIND - 1 ))
     OPTIND=1
 
-    [ -n "$1" ] || shpy_die "Error: Missing spy name"
+    [ $# -eq 0 ] && shpy_die "Error: Missing spy name"
 
     _shpyResetSpy "$1"
     _shpySpySetReturnValue "$1" "${val:-0}"
@@ -144,7 +144,7 @@ examineNextSpyCall() {
 }
 
 cleanupSpies() {
-    if [ -n "$_shpy_spies_dir" ]; then
+    if [ -n "${_shpy_spies_dir+is_set}" ]; then
         shpy_remove_dir_tree "$_shpy_spies_dir" || shpy_die "Error: \`shpy_remove_dir_tree '$_shpy_spies_dir'\` failed"
     fi
 }
diff --git a/t/test_cleanupSpies b/t/test_cleanupSpies
new file mode 100755
index 0000000..21f521e
--- /dev/null
+++ b/t/test_cleanupSpies
@@ -0,0 +1,48 @@
+#!/bin/sh
+
+readonly TEST_DIR="$(dirname "$0")"
+
+# shellcheck source=/dev/null
+. "$TEST_DIR/../shpy"
+# shellcheck source=/dev/null
+. "$TEST_DIR/../shpy-shunit2"
+
+testCleanupSpies_RemovesTmpDirectory() {
+  createSpy foo
+
+  # shellcheck disable=SC2154
+  assertNotNull "${_shpy_spies_dir}"
+  [ -d "${_shpy_spies_dir}" ] || fail "Temporary directory does not exist"
+
+  cleanupSpies
+
+  [ ! -d "${_shpy_spies_dir}" ] || fail "Temporary directory should have been removed"
+}
+
+testWorksUnderNoUnsetOption() {
+  [ -d "${_shpy_spies_dir}" ] && shpy_remove_dir_tree "${_shpy_spies_dir}"
+
+  unset -v _shpy_spies_dir
+  unset -v _shpy_inited
+
+  set -o nounset
+
+  createSpy foo
+
+  cleanupSpies || fail "Should exit cleanly"
+}
+
+testDoesNotFailIfNoSpiesCreated() {
+  [ -d "${_shpy_spies_dir}" ] && shpy_remove_dir_tree "${_shpy_spies_dir}"
+
+  unset -v _shpy_spies_dir
+  unset -v _shpy_inited
+
+  set -o nounset
+
+  cleanupSpies || fail "Should exit cleanly"
+}
+
+
+# shellcheck source=/dev/null
+. "$TEST_DIR/shunit2"
diff --git a/t/test_createSpy b/t/test_createSpy
index ee10664..e172de3 100755
--- a/t/test_createSpy
+++ b/t/test_createSpy
@@ -2,6 +2,8 @@
 
 readonly TEST_DIR="$(dirname "$0")"
 
+set -o nounset
+
 # shellcheck source=/dev/null
 . "$TEST_DIR/../shpy"