Add test

tests/BVH.ResultVolume.test.js

@@ -0,0 +1,23 @@
+import { Brush, Evaluator, SUBTRACTION, computeMeshVolume } from '../src';
+import { SphereGeometry } from 'three';
+
+describe( 'CSG', () => {
+
+	it( 'subtraction should result in the volume of difference.', () => {
+
+		const sphere1 = new Brush( new SphereGeometry() );
+		const sphere2 = new Brush( new SphereGeometry() );
+		sphere2.scale.setScalar( 0.5 );
+		sphere2.updateMatrixWorld( true );
+
+		const evaluator = new Evaluator();
+		const result = evaluator.evaluate( sphere1, sphere2, SUBTRACTION );
+
+		const vol1 = computeMeshVolume( sphere1 );
+		const vol2 = computeMeshVolume( sphere2 );
+		const finalVol = computeMeshVolume( result );
+		expect( finalVol ).toBeCloseTo( vol1 - vol2, 10 );
+
+	} );
+
+} );