add simple unit tests

Author: GarboMuffin

test/unit/tw_external.js

@@ -0,0 +1,36 @@
+const external = require('../../src/extension-support/tw-external');
+const {test} = require('tap');
+
+test('importModule', t => {
+    external.importModule('data:text/javascript;,export%20default%201').then(mod => {
+        t.equal(mod.default, 1);
+        t.end();
+    });
+});
+
+test('fetch', t => {
+    external.fetch('data:text/plain;,test').then(res => {
+        res.text().then(text => {
+            t.equal(text, 'test');
+            t.end();
+        });
+    });
+});
+
+// Node.js does not support FileReader (yet?) so not really possible to properly test dataURL
+
+test('blob', t => {
+    external.blob('data:text/plain;,test').then(blob => {
+        blob.text().then(blobText => {
+            t.equal(blobText, 'test');
+            t.end();
+        });
+    });
+});
+
+test('evalAndReturn', t => {
+    external.evalAndReturn('data:text/plain;,var%20x=20', 'x').then(result => {
+        t.equal(result, 20);
+        t.end();
+    });
+});