Update __init__.py

Author: bxngyn

jar/__init__.py

@@ -78,6 +78,7 @@ def test_number_functions():
             "test_jar.py does not contain at least four valid functions"
         )
 
+
 @check50.check(test_student_file_passes)
 def test_named_functions():
     """test_jar.py defines test_init, test_str, test_deposit, and test_withdraw"""
@@ -89,3 +90,15 @@ def test_named_functions():
         matches = re.search(rf"def\s+{func}\s*\(", contents)
         if not matches:
             raise check50.Failure(f"{func} not found in test_jar.py")
+
+
+@check50.check(test_student_file_passes)
+def test_valid_testing():
+    """test_jar.py contains implemented functions"""
+    
+    # https://stackoverflow.com/questions/845058/how-to-get-the-line-count-of-a-large-file-cheaply-in-python
+    with open("test_jar.py", "rbU") as t:
+        num_lines = sum(1 for _ in t)
+
+    if num_lines < 20:
+        raise check50.Failure("test_jar.py functions not implemented")