Add tests for intersectsExtent/getExtent

This commit adds tests for `intersectsExtent` of Point, LineString, Polygon,
MultiPoint, MultiLineString, MultiPolygon and GeometryCollection.

It also adds a basic test for `getExtent` of MultiPolygon

test/spec/ol/geom/multilinestring.test.js

@@ -88,6 +88,18 @@ describe('ol.geom.MultiLineString', function() {
 
     });
 
+    describe('#intersectsExtent()', function() {
+
+      it('returns true for intersecting part of lineString', function() {
+        expect(multiLineString.intersectsExtent([1, 2, 2, 3])).to.be(true);
+      });
+
+      it('returns false for non-matching extent within own extent', function() {
+        expect(multiLineString.intersectsExtent([1, 7, 2, 8])).to.be(false);
+      });
+
+    });
+
   });
 
   describe('construct with 3D coordinates', function() {