Give interactions a reference to the map

This is in line with what we do for controls and overlays.  A follow-up change will add calls to `setMap` when interactions are added to a map.

test/spec/ol/interaction/interaction.test.js

@@ -0,0 +1,50 @@
+goog.provide('ol.test.interaction.Interaction');
+
+describe('ol.interaction.Interaction', function() {
+
+  describe('constructor', function() {
+
+    it('creates a new interaction', function() {
+      var interaction = new ol.interaction.Interaction();
+      expect(interaction).to.be.a(ol.interaction.Interaction);
+    });
+
+  });
+
+  describe('#getMap()', function() {
+
+    it('retrieves the associated map', function() {
+      var map = new ol.Map({});
+      var interaction = new ol.interaction.Interaction();
+      interaction.setMap(map);
+      expect(interaction.getMap()).to.be(map);
+    });
+
+    it('returns null if no map', function() {
+      var interaction = new ol.interaction.Interaction();
+      expect(interaction.getMap()).to.be(null);
+    });
+
+  });
+
+  describe('#setMap()', function() {
+
+    it('allows a map to be set', function() {
+      var map = new ol.Map({});
+      var interaction = new ol.interaction.Interaction();
+      interaction.setMap(map);
+      expect(interaction.getMap()).to.be(map);
+    });
+
+    it('accepts null', function() {
+      var interaction = new ol.interaction.Interaction();
+      interaction.setMap(null);
+      expect(interaction.getMap()).to.be(null);
+    });
+
+  });
+
+});
+
+goog.require('ol.Map');
+goog.require('ol.interaction.Interaction');