Add ability to extend (pad) the edges of an image

test/unit/extend.js

@@ -0,0 +1,52 @@
+'use strict';
+
+var assert = require('assert');
+
+var sharp = require('../../index');
+var fixtures = require('../fixtures');
+
+describe('Extend', function () {
+
+  it('extend all sides equally with RGB', function(done) {
+    sharp(fixtures.inputJpg)
+      .resize(120)
+      .background({r: 255, g: 0, b: 0})
+      .extend(10)
+      .toBuffer(function(err, data, info) {
+        if (err) throw err;
+        assert.strictEqual(140, info.width);
+        assert.strictEqual(118, info.height);
+        fixtures.assertSimilar(fixtures.expected('extend-equal.jpg'), data, done);
+      });
+  });
+
+  it('extend sides unequally with RGBA', function(done) {
+    sharp(fixtures.inputPngWithTransparency16bit)
+      .resize(120)
+      .background({r: 0, g: 0, b: 0, a: 0})
+      .extend({top: 50, bottom: 0, left: 10, right: 35})
+      .toBuffer(function(err, data, info) {
+        if (err) throw err;
+        assert.strictEqual(165, info.width);
+        assert.strictEqual(170, info.height);
+        fixtures.assertSimilar(fixtures.expected('extend-unequal.png'), data, done);
+      });
+  });
+
+  it('missing parameter fails', function() {
+    assert.throws(function() {
+      sharp().extend();
+    });
+  });
+  it('negative fails', function() {
+    assert.throws(function() {
+      sharp().extend(-1);
+    });
+  });
+  it('partial object fails', function() {
+    assert.throws(function() {
+      sharp().extend({top: 1});
+    });
+  });
+
+});