From 87b303d54cb5fc2b7acf8b3b4d43edb72db29898 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Piotr=20Gai=C5=84ski?= <dociebieaniuszlem@gmail.com>
Date: Thu, 9 Jan 2020 08:43:36 +0100
Subject: [PATCH] Add just mean test

---
 sklearn/utils/tests/test_extmath.py | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/sklearn/utils/tests/test_extmath.py b/sklearn/utils/tests/test_extmath.py
index 427462fda4adc..a40539eb5c19e 100644
--- a/sklearn/utils/tests/test_extmath.py
+++ b/sklearn/utils/tests/test_extmath.py
@@ -469,6 +469,22 @@ def test_incremental_weighted_mean_and_variance_simple():
     assert_almost_equal(var, var_exp)
 
 
+def test_incremental_weighted_mean_and_variance_just_mean():
+    rng = np.random.RandomState(42)
+    mult = 10
+    X = rng.rand(1000, 20)*mult
+    sample_weight = rng.rand(X.shape[0]) * mult
+    mean, var, _ = \
+        _incremental_weighted_mean_and_var(X, sample_weight,
+                                           last_weighted_mean=0,
+                                           last_weighted_variance=None,
+                                           last_weight_sum=0)
+
+    mean_exp = np.average(X, weights=sample_weight, axis=0)
+    assert_almost_equal(mean, mean_exp)
+    assert(var is None)
+
+
 def test_incremental_weighted_mean_and_variance():
 
     # Testing of correctness and numerical stability