run-tests: add 'diff' entry in json report

This patch adds to the json report the "diff" between expected and observed
result. This diff can be useful for automatically filing bug report on failing
tests.

tests/run-tests.py

@@ -1731,7 +1731,9 b' class TextTestRunner(unittest.TextTestRu'
                                     'cuser': ('%0.3f' % timesd[tc.name][0]),
                                     'csys': ('%0.3f' % timesd[tc.name][1]),
                                     'start': ('%0.3f' % timesd[tc.name][3]),
-                                    'end': ('%0.3f' % timesd[tc.name][4])}
+                                    'end': ('%0.3f' % timesd[tc.name][4]),
+                                    'diff': result.faildata.get(tc.name, ''),
+                                    }
                             outcome[tc.name] = tres
                     jsonout = json.dumps(outcome, sort_keys=True, indent=4)
                     fp.writelines(("testreport =", jsonout))

tests/test-run-tests.t

@@ -530,6 +530,7 b' test for --json'
       "test-failure.t": [\{] (re)
           "csys": "\s*[\d\.]{4,5}", ? (re)
           "cuser": "\s*[\d\.]{4,5}", ? (re)
+          "diff": "---.+\+\+\+.+", ? (re)
           "end": "\s*[\d\.]{4,5}", ? (re)
           "result": "failure", ? (re)
           "start": "\s*[\d\.]{4,5}", ? (re)
@@ -538,6 +539,7 b' test for --json'
       "test-skip.t": {
           "csys": "\s*[\d\.]{4,5}", ? (re)
           "cuser": "\s*[\d\.]{4,5}", ? (re)
+          "diff": "", ? (re)
           "end": "\s*[\d\.]{4,5}", ? (re)
           "result": "skip", ? (re)
           "start": "\s*[\d\.]{4,5}", ? (re)
@@ -546,6 +548,7 b' test for --json'
       "test-success.t": [\{] (re)
           "csys": "\s*[\d\.]{4,5}", ? (re)
           "cuser": "\s*[\d\.]{4,5}", ? (re)
+          "diff": "", ? (re)
           "end": "\s*[\d\.]{4,5}", ? (re)
           "result": "success", ? (re)
           "start": "\s*[\d\.]{4,5}", ? (re)
@@ -575,6 +578,7 b' Test that failed test accepted through i'
       "test-failure.t": [\{] (re)
           "csys": "\s*[\d\.]{4,5}", ? (re)
           "cuser": "\s*[\d\.]{4,5}", ? (re)
+          "diff": "", ? (re)
           "end": "\s*[\d\.]{4,5}", ? (re)
           "result": "success", ? (re)
           "start": "\s*[\d\.]{4,5}", ? (re)
@@ -583,6 +587,7 b' Test that failed test accepted through i'
       "test-skip.t": {
           "csys": "\s*[\d\.]{4,5}", ? (re)
           "cuser": "\s*[\d\.]{4,5}", ? (re)
+          "diff": "", ? (re)
           "end": "\s*[\d\.]{4,5}", ? (re)
           "result": "skip", ? (re)
           "start": "\s*[\d\.]{4,5}", ? (re)
@@ -591,6 +596,7 b' Test that failed test accepted through i'
       "test-success.t": [\{] (re)
           "csys": "\s*[\d\.]{4,5}", ? (re)
           "cuser": "\s*[\d\.]{4,5}", ? (re)
+          "diff": "", ? (re)
           "end": "\s*[\d\.]{4,5}", ? (re)
           "result": "success", ? (re)
           "start": "\s*[\d\.]{4,5}", ? (re)