Refactor the CLI. (#5574)

* Enable parameter validation.
* Enable JSON.
* Catch `dmlc::Error`.
* Show help message.

tests/python/test_cli.py

@@ -5,6 +5,7 @@ import platform
 import xgboost
 import subprocess
 import numpy
+import json
 
 
 class TestCLI(unittest.TestCase):
@@ -27,20 +28,23 @@ data = {data_path}
 eval[test] = {data_path}
 '''
 
-    def test_cli_model(self):
-        curdir = os.path.normpath(os.path.abspath(os.path.dirname(__file__)))
-        project_root = os.path.normpath(
-            os.path.join(curdir, os.path.pardir, os.path.pardir))
-        data_path = "{root}/demo/data/agaricus.txt.train?format=libsvm".format(
-            root=project_root)
+    curdir = os.path.normpath(os.path.abspath(os.path.dirname(__file__)))
+    project_root = os.path.normpath(
+        os.path.join(curdir, os.path.pardir, os.path.pardir))
 
+    def get_exe(self):
         if platform.system() == 'Windows':
             exe = 'xgboost.exe'
         else:
             exe = 'xgboost'
-        exe = os.path.join(project_root, exe)
+        exe = os.path.join(self.project_root, exe)
         assert os.path.exists(exe)
+        return exe
 
+    def test_cli_model(self):
+        data_path = "{root}/demo/data/agaricus.txt.train?format=libsvm".format(
+            root=self.project_root)
+        exe = self.get_exe()
         seed = 1994
 
         with tempfile.TemporaryDirectory() as tmpdir:
@@ -102,3 +106,48 @@ eval[test] = {data_path}
                 py_model_bin = fd.read()
 
             assert hash(cli_model_bin) == hash(py_model_bin)
+
+    def test_cli_help(self):
+        exe = self.get_exe()
+        completed = subprocess.run([exe], stdout=subprocess.PIPE)
+        error_msg = completed.stdout.decode('utf-8')
+        ret = completed.returncode
+        assert ret == 1
+        assert error_msg.find('Usage') != -1
+        assert error_msg.find('eval[NAME]') != -1
+
+        completed = subprocess.run([exe, '-V'], stdout=subprocess.PIPE)
+        msg = completed.stdout.decode('utf-8')
+        assert msg.find('XGBoost') != -1
+        v = xgboost.__version__
+        if v.find('SNAPSHOT') != -1:
+            assert msg.split(':')[1].strip() == v.split('-')[0]
+        else:
+            assert msg.split(':')[1].strip() == v
+
+    def test_cli_model_json(self):
+        exe = self.get_exe()
+        data_path = "{root}/demo/data/agaricus.txt.train?format=libsvm".format(
+            root=self.project_root)
+        seed = 1994
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            model_out_cli = os.path.join(
+                tmpdir, 'test_load_cli_model-cli.json')
+            config_path = os.path.join(tmpdir, 'test_load_cli_model.conf')
+
+            train_conf = self.template.format(data_path=data_path,
+                                              seed=seed,
+                                              task='train',
+                                              model_in='NULL',
+                                              model_out=model_out_cli,
+                                              test_path='NULL',
+                                              name_pred='NULL')
+            with open(config_path, 'w') as fd:
+                fd.write(train_conf)
+
+            subprocess.run([exe, config_path])
+            with open(model_out_cli, 'r') as fd:
+                model = json.load(fd)
+
+            assert model['learner']['gradient_booster']['name'] == 'gbtree'