Add spec for ICMP decoder

  - Remove fallacious fields from ICMP class

decode/icmp.js

@@ -1,18 +1,14 @@
 function ICMP() {
-    this.type = null;
-    this.code = null;
-    this.checksum = null;
-    this.id = null;
-    this.sequence = null;
+    this.type = undefined;
+    this.code = undefined;
+    this.checksum = undefined;
 }
 
 // http://en.wikipedia.org/wiki/Internet_Control_Message_Protocol
 ICMP.prototype.decode = function (raw_packet, offset) {
-    this.type = raw_packet[offset];
-    this.code = raw_packet[offset + 1];
-    this.checksum = raw_packet.readUInt16BE(offset + 2); // 2, 3
-    this.id = raw_packet.readUInt16BE(offset + 4); // 4, 5
-    this.sequence = raw_packet.readUInt16BE(offset + 6); // 6, 7
+    this.type = raw_packet[offset++];
+    this.code = raw_packet[offset++];
+    this.checksum = raw_packet.readUInt16BE(offset); // 2, 3
 
     return this;
 };

spec/decode/icmp.spec.js

@@ -0,0 +1,31 @@
+var Icmp = require("../../decode/icmp");
+require("should");
+
+describe("ICMP", function(){
+  var exampleIcmp, instance;
+  beforeEach(function () {
+    exampleIcmp = new Buffer("01020304", "hex");
+    instance = new Icmp();
+  });
+
+  describe("#decode()", function(){
+    it("is a function", function(){
+        instance.decode.should.be.type("function");
+    });
+
+    it("sets the #type to the ICMP type", function() {
+      instance.decode(exampleIcmp, 0);
+      instance.should.have.property("type", 1);
+    });
+
+    it("sets the #code to the ICMP subtype", function() {
+      instance.decode(exampleIcmp, 0);
+      instance.should.have.property("code", 2);
+    });
+
+    it("sets the #checksum to the decoded checksum for the header and data", function() {
+      instance.decode(exampleIcmp, 0);
+      instance.should.have.property("checksum", 772);
+    });
+  });
+});