diff -r d0b9e9803caf -r 56acc4250900 tests/test-simplekeyvaluefile.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/test-simplekeyvaluefile.py	Fri Mar 10 14:33:42 2017 -0800
@@ -0,0 +1,72 @@
+from __future__ import absolute_import
+
+import unittest
+import silenttestrunner
+
+from mercurial import (
+    error,
+    scmutil,
+)
+
+class mockfile(object):
+    def __init__(self, name, fs):
+        self.name = name
+        self.fs = fs
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, *args, **kwargs):
+        pass
+
+    def write(self, text):
+        self.fs.contents[self.name] = text
+
+    def read(self):
+        return self.fs.contents[self.name]
+
+class mockvfs(object):
+    def __init__(self):
+        self.contents = {}
+
+    def read(self, path):
+        return mockfile(path, self).read()
+
+    def readlines(self, path):
+        return mockfile(path, self).read().split('\n')
+
+    def __call__(self, path, mode, atomictemp):
+        return mockfile(path, self)
+
+class testsimplekeyvaluefile(unittest.TestCase):
+    def setUp(self):
+        self.vfs = mockvfs()
+
+    def testbasicwriting(self):
+        d = {'key1': 'value1', 'Key2': 'value2'}
+        scmutil.simplekeyvaluefile(self.vfs, 'kvfile').write(d)
+        self.assertEqual(sorted(self.vfs.read('kvfile').split('\n')),
+                         ['', 'Key2=value2', 'key1=value1'])
+
+    def testinvalidkeys(self):
+        d = {'0key1': 'value1', 'Key2': 'value2'}
+        with self.assertRaisesRegexp(error.ProgrammingError,
+                                     "keys must start with a letter.*"):
+            scmutil.simplekeyvaluefile(self.vfs, 'kvfile').write(d)
+        d = {'key1@': 'value1', 'Key2': 'value2'}
+        with self.assertRaisesRegexp(error.ProgrammingError, "invalid key.*"):
+            scmutil.simplekeyvaluefile(self.vfs, 'kvfile').write(d)
+
+    def testinvalidvalues(self):
+        d = {'key1': 'value1', 'Key2': 'value2\n'}
+        with self.assertRaisesRegexp(error.ProgrammingError, "invalid val.*"):
+            scmutil.simplekeyvaluefile(self.vfs, 'kvfile').write(d)
+
+    def testcorruptedfile(self):
+        self.vfs.contents['badfile'] = 'ababagalamaga\n'
+        with self.assertRaisesRegexp(error.CorruptedState,
+                                     "dictionary.*element.*"):
+            scmutil.simplekeyvaluefile(self.vfs, 'badfile').read()
+
+if __name__ == "__main__":
+    silenttestrunner.main(__name__)