D-Bus Testing: added assertEqualDiff()

Replaces the diffStrings() from the previous commit. Renamed it
because it really is specifying an assertion and moved it to
DBusUtil because it may be useful outside of the command line
testing.

Also made sure that the diff is part of the assertion because then it
will be repeated when listing the failure.

test/test-dbus.py

@@ -832,6 +832,24 @@ class DBusUtil(Timeout):
             self.assertFalse("error" in reports[0])
         return reports[0]
 
+    def assertEqualDiff(self, expected, res):
+        '''Like assertEqual(), but raises an error which contains a
+        diff of the two parameters. Useful when they are long strings
+        (will be split at newlines automatically) or lists (compared
+        as-is). Very similar to Python's 2.7 unittest, but also works
+        for older Python releases and allows comparing strings against lists.'''
+        def splitlines(str):
+            '''split any object which looks like a string == has splitlines'''
+            if 'splitlines' in dir(str):
+                return str.splitlines(True)
+            else:
+                return str
+        expected = splitlines(expected)
+        res = splitlines(res)
+        if expected != res:
+            diff = ''.join(difflib.Differ().compare(expected, res))
+            self.fail('differences between expected and actual text\n\n' + diff)
+
 class TestDBusServer(unittest.TestCase, DBusUtil):
     """Tests for the read-only Server API."""
 
@@ -3514,14 +3532,6 @@ class TestCmdline(unittest.TestCase, DBusUtil):
                                         "SSLServerCertificates = ",
                                         "SSLServerCertificates = ")
 
-    def diffStrings(self, expected, res):
-        if expected != res:
-            for line in difflib.context_diff(expected.splitlines(True), res.splitlines(True), fromfile = "expected", tofile = "actual"):
-                sys.stdout.write(line)
-            self.assertTrue(False)
-
-
-
     def testFramework(self):
         """TestCmdline.testFramework - tests whether utility functions work"""
         content = "baz:line\n" \
@@ -3545,7 +3555,7 @@ class TestCmdline(unittest.TestCase, DBusUtil):
 
         createFiles(self.testdir, content)
         res = scanFiles(self.testdir)
-        self.diffStrings(filtered, res)
+        self.assertEqualDiff(filtered, res)
         randomUUID = "deviceId = syncevolution-blabla\n"
         fixedUUID = "deviceId = fixed-devid\n"
         res = self.removeRandomUUID(randomUUID)
@@ -3567,7 +3577,25 @@ class TestCmdline(unittest.TestCase, DBusUtil):
                    "f:j\n" \
                    "f:a\n"
         res = sortConfig(unsorted)
-        self.diffStrings(expected, res)
+        self.assertEqualDiff(expected, res)
+
+        # test DBusUtil.assertEqualDiff()
+        try:
+            self.assertEqualDiff('foo\nbar\n', 'foo\nxxx\nbar\n')
+        except AssertionError, ex:
+            expected = '''differences between expected and actual text
+
+  foo
++ xxx
+  bar
+'''
+            self.assertTrue(str(ex).endswith(expected), 'actual exception differs\n' + str(ex))
+        else:
+            self.fail('''DBusUtil.assertEqualDiff() did not detect diff''')
+
+        self.assertEqualDiff('foo\nbar', [ 'foo\n', 'bar' ])
+        self.assertEqualDiff([ 'foo\n', 'bar' ], 'foo\nbar')
+        self.assertEqualDiff([ 'foo\n', 'bar' ], [ 'foo\n', 'bar' ])
 
         lines = "a\nb\nc\n"
         lastline = "c\n"