Add JSON schema to model dump. (#5660)

tests/cpp/tree/test_tree_model.cc

@@ -151,6 +151,10 @@ TEST(Tree, DumpJson) {
 
   str = tree.DumpModel(fmap, false, "json");
   ASSERT_EQ(str.find("cover"), std::string::npos);
+
+
+  auto j_tree = Json::Load({str.c_str(), str.size()});
+  ASSERT_EQ(get<Array>(j_tree["children"]).size(), 2);
 }
 
 TEST(Tree, DumpText) {

tests/python/test_basic_models.py

@@ -325,7 +325,7 @@ class TestModels(unittest.TestCase):
         assert locale.getpreferredencoding(False) == loc
 
     @pytest.mark.skipif(**tm.no_json_schema())
-    def test_json_schema(self):
+    def test_json_io_schema(self):
         import jsonschema
         model_path = 'test_json_schema.json'
         path = os.path.dirname(
@@ -342,3 +342,35 @@ class TestModels(unittest.TestCase):
         jsonschema.validate(instance=json_model(model_path, parameters),
                             schema=schema)
         os.remove(model_path)
+
+    @pytest.mark.skipif(**tm.no_json_schema())
+    def test_json_dump_schema(self):
+        import jsonschema
+
+        def validate_model(parameters):
+            X = np.random.random((100, 30))
+            y = np.random.randint(0, 4, size=(100,))
+
+            parameters['num_class'] = 4
+            m = xgb.DMatrix(X, y)
+
+            booster = xgb.train(parameters, m)
+            dump = booster.get_dump(dump_format='json')
+
+            for i in range(len(dump)):
+                jsonschema.validate(instance=json.loads(dump[i]),
+                                    schema=schema)
+
+        path = os.path.dirname(
+            os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+        doc = os.path.join(path, 'doc', 'dump.schema')
+        with open(doc, 'r') as fd:
+            schema = json.load(fd)
+
+        parameters = {'tree_method': 'hist', 'booster': 'gbtree',
+                      'objective': 'multi:softmax'}
+        validate_model(parameters)
+
+        parameters = {'tree_method': 'hist', 'booster': 'dart',
+                      'objective': 'multi:softmax'}
+        validate_model(parameters)