From e1560765392121ec3bddbb17f46125ac9b858e56 Mon Sep 17 00:00:00 2001
From: Marcin Michalski <evulmastah@gmail.com>
Date: Wed, 7 Mar 2018 23:16:25 +0100
Subject: [PATCH] Add DecisionTreeLeaf.getNodeImpurityDecrease test (#261)

---
 .../DecisionTree/DecisionTreeLeafTest.php     | 24 +++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/tests/Classification/DecisionTree/DecisionTreeLeafTest.php b/tests/Classification/DecisionTree/DecisionTreeLeafTest.php
index abcf10d..e694878 100644
--- a/tests/Classification/DecisionTree/DecisionTreeLeafTest.php
+++ b/tests/Classification/DecisionTree/DecisionTreeLeafTest.php
@@ -23,4 +23,28 @@ class DecisionTreeLeafTest extends TestCase
 
         $this->assertEquals('<table ><tr><td colspan=3 align=center style=\'border:1px solid;\'><b>col_0 =1</b><br>Gini: 0.00</td></tr><tr><td></td><td>&nbsp;</td><td valign=top align=right><b>No |</b><br><table ><tr><td colspan=3 align=center style=\'border:1px solid;\'><b>col_1 <= 2</b><br>Gini: 0.00</td></tr></table></td></tr></table>', $leaf->getHTML());
     }
+
+    public function testNodeImpurityDecreaseShouldBeZeroWhenLeafIsTerminal(): void
+    {
+        $leaf = new DecisionTreeLeaf();
+        $leaf->isTerminal = true;
+
+        $this->assertEquals(0.0, $leaf->getNodeImpurityDecrease(1));
+    }
+
+    public function testNodeImpurityDecrease(): void
+    {
+        $leaf = new DecisionTreeLeaf();
+        $leaf->giniIndex = 0.5;
+        $leaf->records = [1, 2, 3];
+
+        $leaf->leftLeaf = new DecisionTreeLeaf();
+        $leaf->leftLeaf->records = [5, 2];
+
+        $leaf->rightLeaf = new DecisionTreeLeaf();
+        $leaf->rightLeaf->records = [];
+        $leaf->rightLeaf->giniIndex = 0.3;
+
+        $this->assertSame(0.75, $leaf->getNodeImpurityDecrease(2));
+    }
 }