test: protect the run-tests.py --json test behind an hghave rule

test: protect the run-tests.py --json test behind an hghave rule

We add a rules to detect availability of a json module and skip if json is not
available.

--- a/tests/hghave.py	Mon Sep 29 17:23:38 2014 -0500
+++ b/tests/hghave.py	Thu Sep 18 11:43:47 2014 -0700
@@ -281,6 +281,18 @@
 def has_python243():
     return sys.version_info >= (2, 4, 3)
 
+@check("json", "some json module available")
+def has_json():
+    try:
+        if sys.version_info < (2, 7):
+            import simplejson as json
+        else:
+            import json
+        json.dumps
+        return True
+    except ImportError:
+        return False
+
 @check("outer-repo", "outer repo")
 def has_outer_repo():
     # failing for other reasons than 'no repo' imply that there is a repo

--- a/tests/test-run-tests.t	Mon Sep 29 17:23:38 2014 -0500
+++ b/tests/test-run-tests.t	Thu Sep 18 11:43:47 2014 -0700
@@ -369,6 +369,8 @@
   Skipped test-failure.t: blacklisted
   # Ran 0 tests, 2 skipped, 0 warned, 0 failed.
 
+#if json
+
 test for --json
 ==================
 
@@ -412,3 +414,5 @@
           "time": "\s*[\d\.]{5}" (re)
       }
   } (no-eol)
+
+#endif