Add DecisionTreeLeaf.getNodeImpurityDecrease test (#261)

Author: marmichalski

tests/Classification/DecisionTree/DecisionTreeLeafTest.php

@@ -23,4 +23,28 @@ public function testHTMLOutput(): void
 
         $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));
+    }
 }