adding testcases to cover situations where the input upwards step count is zero

Author: erosb

core/src/main/java/org/everit/json/schema/internal/RelativeJsonPointerFormatValidator.java

@@ -62,8 +62,15 @@ private char curr() {
         }
 
         private void parseUpwardsStepCount() throws ParseException {
-            if (!isDigit(curr()) || curr() == '0') {
+            if (!isDigit(curr())) {
                 fail();
+            } else if (curr() == '0') {
+                next();
+                if (curr() == '/' || curr() == '#' || curr() == EOF) {
+                    pos--;
+                } else {
+                    fail();
+                }
             }
             for (char current = next(); isDigit(current) && pos < input.length(); current = next())
                 ;

core/src/test/java/org/everit/json/schema/internal/RelativeJsonPointerFormatValidatorTest.java

@@ -76,7 +76,22 @@ public void noUpwardsStepCount() {
     }
 
     @Test
-    public void leadingZeroFailure()  {
+    public void leadingZeroFailure() {
         assertFailure("0123", SUBJECT, "[0123] is not a valid relative JSON Pointer");
     }
+
+    @Test
+    public void onlyLeadingZero() {
+        assertSuccess("0", SUBJECT);
+    }
+
+    @Test
+    public void upwardsStepCountIsZeroFollowedByPointer() {
+        assertSuccess("0/a/b", SUBJECT);
+    }
+
+    @Test
+    public void upwardsStepCountIsZeroFollowedByHashmark() {
+        assertSuccess("0#", SUBJECT);
+    }
 }