diff --git a/Makefile b/Makefile
index 8a82fa3..8eb1a81 100644
--- a/Makefile
+++ b/Makefile
@@ -2,6 +2,7 @@ all:
 	@echo "Targets:"
 	@echo "  pypi        Build distributions and upload them to PyPI."
 	@echo "  uptime.zip  Build docs and zip them for manual upload to PyPI."
+	@echo "  tests       Run the unit tests."
 	@echo "  clean       Clear out temporary cruft."
 
 .PHONY: pypi
@@ -13,6 +14,14 @@ uptime.zip: doc/index.rst doc/conf.py
 	cd doc; $(MAKE) clean html
 	cd doc/_build/html; zip -r ../../../uptime.zip *
 
+.PHONY: tests
+tests:
+	@python --version
+	@python tests/uptime_tests.py
+	@echo
+	@python3 --version
+	@python3 tests/uptime_tests.py
+
 .PHONY: clean
 clean:
 	cd doc; $(MAKE) clean
diff --git a/tests/uptime_tests.py b/tests/uptime_tests.py
new file mode 100755
index 0000000..5be33c5
--- /dev/null
+++ b/tests/uptime_tests.py
@@ -0,0 +1,121 @@
+#!/usr/bin/env python
+# coding: utf8
+
+import imp
+import sys
+import time
+import unittest
+
+sys.path.insert(0, '.')
+
+import src as uptime
+
+
+boottime_helpers = [f for f in vars(uptime) if f.startswith('_boottime_')]
+uptime_helpers = [f for f in vars(uptime) if f.startswith('_uptime_')]
+
+
+class NormalTest(unittest.TestCase):
+    """
+    This class just calls each of the functions normally and ensures they don't
+    do dumb things like throw exceptions or return complex numbers.
+    """
+    def tearDown(self):
+        """
+        __boottime affects how boottime() and its helpers work, and it may be
+        set as a side-effect by any function. To be on the safe side, just
+        reload the whole module every time.
+        """
+        imp.reload(uptime)
+
+    def basic_test(self, func, rettype):
+        """
+        Calls a given function and checks if it returns None or something of
+        type rettype.
+        """
+        ret = func()
+        self.assertTrue(ret is None or isinstance(ret, rettype))
+
+    def __getattr__(self, name):
+        # I really don't feel like writing and maintaining over a dozen
+        # essentially identical methods, and if there's a cleaner way to do
+        # this, I couldn't find it in the unittest docs.
+        if name.startswith('test_'):
+            func = name[5:]
+            if func == 'uptime' or func in uptime_helpers:
+                rettype = float
+            elif func == 'boottime' or func in boottime_helpers:
+                rettype = time.struct_time
+            else:
+                raise AttributeError()
+            return lambda: self.basic_test(getattr(uptime, func), rettype)
+        else:
+            return unittest.TestCase.__getattr__(self, name)
+
+class BrokenCtypesTest(NormalTest):
+    """
+    It's ridiculous how many platforms don't have ctypes. This class simulates
+    that.
+    """
+    def setUpClass(self):
+        uptime.ctypes = None
+        delattr(uptime, 'struct')
+        delattr(uptime, 'os')
+
+
+def run_suite(suite):
+    """
+    unittest is basically a disaster, so let's do this ourselves.
+    """
+    sys.stdout.write('Running %d tests... \n' % tests.countTestCases())
+
+    res = unittest.TestResult()
+    suite.run(res)
+
+    if res.wasSuccessful():
+        sys.stdout.write('Finished without errors.\n')
+        return
+
+    sys.stdout.write('\n')
+    for problems, kind in ((res.errors, 'error'),
+                           (res.failures, 'failure')):
+        if len(problems):
+            head = '%d %s%s' % (len(problems),
+                                kind,
+                                's' if len(problems) != 1 else '')
+            sys.stdout.write('\033[1;31m%s\n%s\033[0m\n' %
+                             (head, '⎻' * len(head)))
+
+        for problem in problems:
+            func = problem[0]._testMethodName[5:]
+            environ = ' (broken ctypes)' if isinstance(problem[0],
+                                                       BrokenCtypesTest) \
+                                         else ''
+            sys.stdout.write(
+                '• \033[1m%s%s\033[0m failed with message:\n\n%s\n\n' %
+                (func, environ, '\n'.join(map(lambda s: '    ' + s,
+                                              problem[1].splitlines())))
+            )
+
+    sys.stdout.write('%d tests completed successfully.\n' %
+                     (res.testsRun - len(res.failures) - len(res.errors)))
+
+
+if __name__ == '__main__':
+    tests = unittest.TestSuite()
+
+    # uptime tests
+    tests.addTests([NormalTest('test_uptime'),
+                    BrokenCtypesTest('test_uptime')])
+    for helper in uptime_helpers:
+        tests.addTests([NormalTest('test_%s' % helper),
+                        BrokenCtypesTest('test_%s' % helper)])
+
+    # boottime tests
+    tests.addTests([NormalTest('test_boottime'),
+                    BrokenCtypesTest('test_boottime')])
+    for helper in boottime_helpers:
+        tests.addTests([NormalTest('test_%s' % helper),
+                        BrokenCtypesTest('test_%s' % helper)])
+
+    run_suite(tests)