added test_cache

tests/test_helpers.py

@@ -5,7 +5,7 @@ import pytest
 
 from pytube import helpers
 from pytube.exceptions import RegexMatchError
-from pytube.helpers import deprecated
+from pytube.helpers import deprecated, cache
 
 
 def test_regex_search_no_match():
@@ -28,9 +28,27 @@ def test_deprecated(warn):
     @deprecated("oh no")
     def deprecated_function():
         return None
+
     deprecated_function()
     warn.assert_called_with(
         "Call to deprecated function deprecated_function (oh no).",
         category=DeprecationWarning,
         stacklevel=2,
     )
+
+
+def test_cache():
+    call_count = 0
+
+    @cache
+    def cached_func(stuff):
+        nonlocal call_count
+        call_count += 1
+        return stuff
+
+    cached_func("hi")
+    cached_func("hi")
+    cached_func("bye")
+    cached_func("bye")
+
+    assert call_count == 2