test: Add basic test

tests/test_lib.py

@@ -0,0 +1,16 @@
+import time
+
+from retry_later import retry_later
+
+
+@retry_later()
+def write_to_file(file_name: str, body: str):
+    with open(file_name, "w") as f:
+        f.write(body)
+
+
+def test_success_once():
+    write_to_file("test.txt", "hello world")
+    time.sleep(5)
+    with open("test.txt") as f:
+        assert "hello world" in f.readlines()