diff --git a/package.json b/package.json
index 7aa7a73..ac5c57a 100644
--- a/package.json
+++ b/package.json
@@ -8,10 +8,11 @@
     "url": "https://github.com/dmester/canvas-renderer"
   },
   "devDependencies": {
-    "tap": "^10.7.0"
+    "tap": "^12.1.1",
+    "pngjs": "^3.3.3"
   },
   "scripts": {
-    "test": "tap tests/*.js"
+    "test": "tap tests/*Tests.js"
   },
   "bugs": {
     "url": "https://github.com/dmester/canvas-renderer/issues"
diff --git a/tests/colorUtils.js b/tests/colorUtilsTests.js
similarity index 100%
rename from tests/colorUtils.js
rename to tests/colorUtilsTests.js
diff --git a/tests/pngAssert.js b/tests/pngAssert.js
new file mode 100644
index 0000000..9edc3d1
--- /dev/null
+++ b/tests/pngAssert.js
@@ -0,0 +1,82 @@
+/**
+ * canvas-renderer
+ * https://github.com/dmester/canvas-renderer
+ * 
+ * Copyright (c) 2017-2018 Daniel Mester Pirttijärvi
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining 
+ * a copy of this software and associated documentation files (the 
+ * "Software"), to deal in the Software without restriction, including 
+ * without limitation the rights to use, copy, modify, merge, publish, 
+ * distribute, sublicense, and/or sell copies of the Software, and to 
+ * permit persons to whom the Software is furnished to do so, subject to 
+ * the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be 
+ * included in all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF 
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. 
+ * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY 
+ * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, 
+ * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE 
+ * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+ 
+"use strict";
+
+/**
+ * This module will extend tap with the assert 
+ * tap.equalPng(found : Buffer, wanted : Buffer, msg, extra)
+ */
+
+const pngjs = require("pngjs");
+
+function createDataUri(buffer) {
+    return "data:image/png;base64," + buffer.toString("base64");
+}
+
+function formatPixel(data, i) {
+    i -= i % 4;
+    return `rgba(${data[i]}, ${data[i + 1]}, ${data[i + 2]}, ${data[i + 3]})`;
+}
+
+function register(tap) {
+    tap.Test.prototype.addAssert("equalPng", 2, function (found, wanted, message, extra) {
+        message = message || "PNG should be equal";
+
+        var foundPng = pngjs.PNG.sync.read(found);
+        var wantedPng = pngjs.PNG.sync.read(wanted);
+        
+        if (foundPng.width != wantedPng.width ||
+            foundPng.height != wantedPng.height ||
+            foundPng.data.length != wantedPng.data.length
+        ) {
+            extra.found = createDataUri(found);
+            extra.wanted = createDataUri(wanted);
+            return this.fail(message, extra);
+        }
+
+        for (var i = 0; i < foundPng.data.length; i++) {
+            // Allow some difference due to rounding errors
+            if (Math.abs(foundPng.data[i] - wantedPng.data[i]) > 2) {
+                extra.found = createDataUri(found);
+                extra.wanted = createDataUri(wanted);
+
+                var x = i % foundPng.width;
+                var y = (i / foundPng.width) | 0;
+
+                extra.foundPixel = formatPixel(foundPng.data, i);
+                extra.wantedPixel = formatPixel(wantedPng.data, i);
+                extra.note = `Difference at pixel { x: ${x}, y: ${y} }.`;
+
+                return this.fail(message, extra);
+            }
+        }
+
+        return this.pass(message, extra);
+    })
+}
+
+module.exports = register;
diff --git a/tests/trueColorTest.js b/tests/trueColorTests.js
similarity index 92%
rename from tests/trueColorTest.js
rename to tests/trueColorTests.js
index 270fdab..8547289 100644
--- a/tests/trueColorTest.js
+++ b/tests/trueColorTests.js
@@ -40,6 +40,7 @@
 const fs = require("fs");
 const tap = require("tap");
 const canvasRenderer = require("../index");
+require("./pngAssert")(tap);
 
 var canvas = canvasRenderer.createCanvas(1000, 1000);
 canvas.backColor = "#abcdefff";
@@ -62,6 +63,5 @@ ctx.arc(400 + radius, 250 + radius, radius, 0, Math.PI * 2, false); // last argu
 ctx.closePath();
 ctx.fill();
 
-var expected = fs.readFileSync(__dirname + "/expected-truecolor.png");
-var expectedB64 = Buffer.from(expected).toString("base64");
-tap.equal("data:image/png;base64," + expectedB64, canvas.toDataURL());
+var wanted = fs.readFileSync(__dirname + "/expected-truecolor.png");
+tap.equalPng(canvas.toPng(), wanted);
diff --git a/tests/visualTest.js b/tests/visualTests.js
similarity index 95%
rename from tests/visualTest.js
rename to tests/visualTests.js
index 55742e4..3adad4d 100644
--- a/tests/visualTest.js
+++ b/tests/visualTests.js
@@ -35,6 +35,7 @@
 const fs = require("fs");
 const tap = require("tap");
 const canvasRenderer = require("../index");
+require("./pngAssert")(tap);
 
 
 var canvas;
@@ -172,7 +173,5 @@ ctx.lineTo(5, 95);
 ctx.closePath();
 ctx.fill();
 
-var expected = fs.readFileSync(__dirname + "/expected.png");
-var expectedB64 = Buffer.from(expected).toString("base64");
-tap.equal("data:image/png;base64," + expectedB64, canvas.toDataURL());
-
+var wanted = fs.readFileSync(__dirname + "/expected.png");
+tap.equalPng(canvas.toPng(), wanted);