Ensure IDs are sorted prior to selecting next

lib/usb/usb_daemon.js

@@ -225,7 +225,7 @@ function USBDaemon() {
   this._nextID = () => {
 
     // Get all currently used ids, what's the first available?
-    var usedIDs = this.getIDsInUse();
+    var usedIDs = this.getIDsInUse().sort();
     var prev;
     var cur;
 

test/unit/daemon.js

@@ -0,0 +1,62 @@
+module.exports['Daemon._nextID'] = {
+  setUp: function(done) {
+    this.sandbox = sinon.sandbox.create();
+    done();
+  },
+
+  tearDown: function(done) {
+    this.sandbox.restore();
+    done();
+  },
+
+  // Returns the next element in the list when ordered with no gaps
+  selectSubsequentId: function(test) {
+    test.expect(1);
+    this.getIDsInUse = this.sandbox.stub(Daemon, 'getIDsInUse').returns([0, 1, 2]);
+    var next = Daemon._nextID();
+    test.equal(next, 3);
+    test.done();
+  },
+
+  // Detects gaps at the front of the id array. Returns first element in gap
+  selectMissingId: function(test) {
+    test.expect(1);
+    this.getIDsInUse = this.sandbox.stub(Daemon, 'getIDsInUse').returns([1, 2]);
+    var next = Daemon._nextID();
+    test.equal(next, 0);
+    test.done();
+  },
+
+  // Detects gap in middle of array
+  detectGapId: function(test) {
+    test.expect(1);
+    this.getIDsInUse = this.sandbox.stub(Daemon, 'getIDsInUse').returns([0, 1, 3]);
+    var next = Daemon._nextID();
+    test.equal(next, 2);
+    test.done();
+  },
+
+  // Can handle out of order ids, returns next after max or first gap
+  handleUnorderedIds: function(test) {
+    test.expect(1);
+    this.getIDsInUse = this.sandbox.stub(Daemon, 'getIDsInUse').returns([2, 3, 1]);
+    var next = Daemon._nextID();
+    test.equal(next, 0);
+    test.done();
+  },
+
+  // Will not return a new id if we already have 255 processes running
+  throwOnMaxIds: function(test) {
+    test.expect(1);
+
+    var maxIds = 255;
+    var idsInUse = [];
+    for (var i = 0; i < maxIds; i++) {
+      idsInUse.push(i);
+    }
+
+    this.getIDsInUse = this.sandbox.stub(Daemon, 'getIDsInUse').returns(idsInUse);
+    test.throws(Daemon._nextID());
+    test.done();
+  }
+};