diff --git a/lib/fs/fs_test.go b/lib/fs/fs_test.go
new file mode 100644
index 0000000000..394cb4a98e
--- /dev/null
+++ b/lib/fs/fs_test.go
@@ -0,0 +1,24 @@
+package fs
+
+import (
+	"testing"
+)
+
+func TestIsTemporaryFileName(t *testing.T) {
+	f := func(s string, resultExpected bool) {
+		t.Helper()
+		result := IsTemporaryFileName(s)
+		if result != resultExpected {
+			t.Fatalf("unexpected IsTemporaryFileName(%q); got %v; want %v", s, result, resultExpected)
+		}
+	}
+	f("", false)
+	f(".", false)
+	f(".tmp", false)
+	f("tmp.123", false)
+	f(".tmp.123.xx", false)
+	f(".tmp.1", true)
+	f("asdf.dff.tmp.123", true)
+	f("asdf.sdfds.tmp.dfd", false)
+	f("dfd.sdfds.dfds.1232", false)
+}