Improve test coverage.

* Test equality of different length strings.
* Add tab to json_pack whitespace test.
* Test json_sprintf with empty result and invalid UTF.
* Test json_get_alloc_funcs with NULL arguments.
* Test invalid arguments.
* Add test_chaos to test allocation failure code paths.
* Remove redundant json_is_string checks from json_string_equal and
  json_string_copy.  Both functions are static and can only be called
  with a json string.

Fixes to issues found by test_chaos:
* Fix crash on OOM in pack_unpack.c:read_string().
* Unconditionally free string in string_create upon allocation failure.
  Update load.c:parse_value() to reflect this.  This resolves a leak on
  allocation failure for pack_unpack.c:pack_string() and
  value.c:json_sprintf().

Although not visible from CodeCoverage these changes significantly
increase branch coverage.  Especially in src/value.c where we previously
covered 67.4% of branches and now cover 96.3% of branches.

1 files changed, 7 insertions, 0 deletions

diff --git a/test/suites/api/test_equal.c b/test/suites/api/test_equal.c
index 7a17636..339bab6 100644
--- a/test/suites/api/test_equal.c
+++ b/test/suites/api/test_equal.c
@@ -74,6 +74,13 @@ static void test_equal_simple()
         fail("unable to create an string");
     if(json_equal(value1, value2))
         fail("json_equal fails for two inequal strings");
+    json_decref(value2);
+
+    value2 = json_string("bar2");
+    if(!value2)
+        fail("unable to create an string");
+    if(json_equal(value1, value2))
+        fail("json_equal fails for two inequal length strings");
 
     json_decref(value1);
     json_decref(value2);