implemented json-pointer format (test added)

Author: erosb

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

@@ -1,13 +1,21 @@
 package org.everit.json.schema.internal;
 
+import static java.lang.String.format;
+
 import java.util.Optional;
 
 import org.everit.json.schema.FormatValidator;
+import org.json.JSONPointer;
 
 public class JsonPointerFormatValidator implements FormatValidator {
 
     @Override public Optional<String> validate(String subject) {
-        throw new UnsupportedOperationException("not yet implemented");
+        try {
+            new JSONPointer(subject);
+            return Optional.empty();
+        } catch (IllegalArgumentException e) {
+            return Optional.of(format("[%s] is not a valid JSON pointer", subject));
+        }
     }
 
     @Override public String formatName() {

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

@@ -0,0 +1,33 @@
+package org.everit.json.schema.internal;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertSame;
+
+import java.util.Optional;
+
+import org.junit.Test;
+
+public class JsonPointerFormatValidatorTest {
+
+    private final JsonPointerFormatValidator subject = new JsonPointerFormatValidator();
+
+    @Test
+    public void uriSuccess() {
+        assertEmpty(subject.validate("#/hello"));
+    }
+
+    private void assertEmpty(Optional<String> actual) {
+        assertSame(Optional.empty(), actual);
+    }
+
+    @Test
+    public void stringSuccess() {
+        assertEmpty(subject.validate("/hello"));
+    }
+
+    @Test
+    public void illegalLeadingCharFailure() {
+        assertEquals(Optional.of("[aaa] is not a valid JSON pointer"), subject.validate("aaa"));
+    }
+
+}

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

@@ -0,0 +1,13 @@
+package org.everit.json.schema.internal;
+
+import org.junit.Test;
+
+public class URIReferenceFormatValidatorTest {
+
+    private final URIReferenceFormatValidator subject = new URIReferenceFormatValidator();
+
+    @Test
+    public void success() {
+
+    }
+}