added test for warnings about unchangeable params

tests/python_package_test/test_basic.py

@@ -1,5 +1,6 @@
 # coding: utf-8
 import os
+import sys
 import tempfile
 import unittest
 
@@ -280,3 +281,77 @@ def check_asserts(data):
         lgb_data.set_weight(sequence)
         lgb_data.set_init_score(sequence)
         check_asserts(lgb_data)
+
+    def test_dataset_update_params_warning(self):
+        default_params = {"max_bin": 100,
+                          "max_bin_by_feature": [20, 10],
+                          "bin_construct_sample_cnt": 10000,
+                          "min_data_in_bin": 1,
+                          "use_missing": False,
+                          "zero_as_missing": False,
+                          "sparse_threshold": 1,
+                          "categorical_feature": [0],
+                          "feature_pre_filter": True,
+                          "min_data_in_leaf": 8}
+        unchangeable_params = {"max_bin": 150,
+                               "max_bin_by_feature": [30, 5],
+                               "bin_construct_sample_cnt": 5000,
+                               "min_data_in_bin": 2,
+                               "use_missing": True,
+                               "zero_as_missing": True,
+                               "sparse_threshold": 0.4,
+                               "categorical_feature": [0, 1],
+                               "feature_pre_filter": False,
+                               "min_data_in_leaf": 3}
+        stdout_backup = os.dup(sys.__stdout__.fileno())
+        log_filename = 'log.txt'
+
+        with open(log_filename, 'a') as stdout_redirect:
+            os.dup2(stdout_redirect.fileno(), sys.__stdout__.fileno())
+            X = np.random.random((100, 2))
+            y = np.random.random(100)
+            lgb_data = lgb.Dataset(X, y)
+            lgb.train(default_params, lgb_data, num_boost_round=5)
+        with open(log_filename, 'r') as stdout_log:
+            log = stdout_log.read()
+            self.assertEqual(log.find('[LightGBM] [Warning] Cannot change '), -1)
+            self.assertEqual(log.find('[LightGBM] [Warning] Reducing `min_data_in_leaf` '
+                                      'with `feature_pre_filter=true` may cause '), -1)
+
+        with open(log_filename, 'a') as stdout_redirect:
+            os.dup2(stdout_redirect.fileno(), sys.__stdout__.fileno())
+            default_params["min_data_in_leaf"] += 1
+            lgb.train(default_params, lgb_data, num_boost_round=5)
+        with open(log_filename, 'r') as stdout_log:
+            log = stdout_log.read()
+            self.assertEqual(log.find('[LightGBM] [Warning] Cannot change '), -1)
+            self.assertEqual(log.find('[LightGBM] [Warning] Reducing `min_data_in_leaf` '
+                                      'with `feature_pre_filter=true` may cause '), -1)
+
+        with open(log_filename, 'a') as stdout_redirect:
+            os.dup2(stdout_redirect.fileno(), sys.__stdout__.fileno())
+            default_params["feature_pre_filter"] = False
+            lgb_data_new = lgb.Dataset(X, y, params=default_params).construct()
+            default_params["min_data_in_leaf"] -= 2
+            lgb.train(default_params, lgb_data_new, num_boost_round=5)
+        with open(log_filename, 'r') as stdout_log:
+            log = stdout_log.read()
+            self.assertEqual(log.find('[LightGBM] [Warning] Cannot change '), -1)
+            self.assertEqual(log.find('[LightGBM] [Warning] Reducing `min_data_in_leaf` '
+                                      'with `feature_pre_filter=true` may cause '), -1)
+
+        with open(log_filename, 'a') as stdout_redirect:
+            os.dup2(stdout_redirect.fileno(), sys.__stdout__.fileno())
+            lgb.train(unchangeable_params, lgb_data, num_boost_round=5)
+        with open(log_filename, 'r') as stdout_log:
+            log = stdout_log.read()
+            for param in unchangeable_params.keys():
+                if param == "min_data_in_leaf":
+                    self.assertNotEqual(log.find('[LightGBM] [Warning] Reducing `min_data_in_leaf` '
+                                                 'with `feature_pre_filter=true` may cause '), -1)
+                else:
+                    self.assertNotEqual(log.find('[LightGBM] [Warning] Cannot '
+                                                 'change {} '.format(param)), -1)
+
+        os.dup2(stdout_backup, sys.__stdout__.fileno())
+        os.remove(log_filename)