diff --git a/unit_tests/doubler.py b/unit_tests/doubler.py
new file mode 100644
index 0000000..4a4faa2
--- /dev/null
+++ b/unit_tests/doubler.py
@@ -0,0 +1,7 @@
+def d(fname="lab99_ex1_easy.expected_input"):
+    with open(fname) as f:
+        n = int(f.read().split()[0])
+        return str(n * 2 + n % 2)
+
+if __name__ == "__main__":
+    print(d())
diff --git a/unit_tests/lab99_ex1_easy.expected_input b/unit_tests/lab99_ex1_easy.expected_input
new file mode 100644
index 0000000..48082f7
--- /dev/null
+++ b/unit_tests/lab99_ex1_easy.expected_input
@@ -0,0 +1 @@
+12
diff --git a/unit_tests/lab99_ex1_easy.expected_output b/unit_tests/lab99_ex1_easy.expected_output
new file mode 100644
index 0000000..a45fd52
--- /dev/null
+++ b/unit_tests/lab99_ex1_easy.expected_output
@@ -0,0 +1 @@
+24
diff --git a/unit_tests/lab99_ex1_hard.expected_input b/unit_tests/lab99_ex1_hard.expected_input
new file mode 100644
index 0000000..77ac6c0
--- /dev/null
+++ b/unit_tests/lab99_ex1_hard.expected_input
@@ -0,0 +1 @@
+4129088901429017650
diff --git a/unit_tests/lab99_ex1_hard.expected_output b/unit_tests/lab99_ex1_hard.expected_output
new file mode 100644
index 0000000..c430968
--- /dev/null
+++ b/unit_tests/lab99_ex1_hard.expected_output
@@ -0,0 +1 @@
+8258177802858035300
diff --git a/unit_tests/lab99_ex1_odd.expected_input b/unit_tests/lab99_ex1_odd.expected_input
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/unit_tests/lab99_ex1_odd.expected_input
@@ -0,0 +1 @@
+1
diff --git a/unit_tests/lab99_ex1_odd.expected_output b/unit_tests/lab99_ex1_odd.expected_output
new file mode 100644
index 0000000..0cfbf08
--- /dev/null
+++ b/unit_tests/lab99_ex1_odd.expected_output
@@ -0,0 +1 @@
+2
diff --git a/unit_tests/lab99_tests.py b/unit_tests/lab99_tests.py
new file mode 100644
index 0000000..4c8e83f
--- /dev/null
+++ b/unit_tests/lab99_tests.py
@@ -0,0 +1,46 @@
+"""
+This file is basic example of a unit test for the labs.
+The TestClass keeps a list of filenames which refer to sample input and
+corresponding output files.
+
+The test_ex1 function tries to pass the contents of each lab99_ex1_*.in to the
+function in the "doubler.py" file; output should match that in lab99_ex1_.*out.
+
+Use ``python3 lab99_tests.py -v`` to run tests.
+"""
+
+
+# ideas:
+# tarball the tests, have students decompress the files
+# make sure students know how to run the tests
+# have .tex read test cases and insert them into the exercises
+# change exercises to require filename as argument to main (use default args)
+#   and have strict return type requirements
+#   can also redirect stdout; or offer students the option
+
+# have the TestCase class make sure filenames are valid
+
+import unittest
+import doubler
+
+def get_output(fname):
+    return fname + ".expected_output"
+
+def get_input(fname):
+    return fname + ".expected_input"
+
+class TestLab99(unittest.TestCase):
+    ex1_test_fnames = ["lab99_ex1_easy", "lab99_ex1_hard", "lab99_ex1_odd"]
+
+    def test_ex1(self):
+        # run subtests, one for each test input
+        for test in TestLab99.ex1_test_fnames:
+            # know which test file caused the code for the exercise to fail
+            with self.subTest(i=test):
+                with open(get_output(test)) as f:
+                    # test the function!
+                    self.assertEqual(doubler.d(get_input(test)),
+                                     f.read().split()[0])
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/unit_tests/lab9_tests.py b/unit_tests/lab9_tests.py
new file mode 100644
index 0000000..6dd7a78
--- /dev/null
+++ b/unit_tests/lab9_tests.py
@@ -0,0 +1,20 @@
+import unittest
+import luhns
+
+class TestLab9(unittest.TestCase):
+    tests = [{"i": "38520000023237", "o": True},
+             {"i": "49927398716", "o": True},
+             {"i": "49927398717", "o": False},
+             {"i": "1234567812345670", "o": False},
+             {"i": "1234567812345678", "o": True}]
+
+    def test_ex1(self):
+        # run subtests, one for each test input
+        for test in TestLab9.tests:
+            # know which test file caused the code for the exercise to fail
+            with self.subTest(i=test):
+                # test the function!
+                self.assertEqual(luhns.validate(test["i"]), test["o"])
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/unit_tests/luhns.py b/unit_tests/luhns.py
new file mode 100644
index 0000000..0b865b4
--- /dev/null
+++ b/unit_tests/luhns.py
@@ -0,0 +1,6 @@
+def validate(card):
+    return {"38520000023237": True,
+     "49927398716": False, #;True,
+     "49927398717": False,
+     "1234567812345670": False,
+     "1234567812345678": True}[card]