Instance mode should not use global functions

See #2999
This is not an exhaustive test but these are the places
we know of at this moment.

Author: Zalastax

test/unit/core/core.js

@@ -197,7 +197,14 @@ suite('Core', function() {
   suite('p5.prototype._createFriendlyGlobalFunctionBinder', function() {
     var noop = function() {};
     var createBinder = p5.prototype._createFriendlyGlobalFunctionBinder;
-    var logMsg, globalObject, bind;
+    var logMsg, globalObject, bind, iframe;
+
+    teardown(function() {
+      if (iframe) {
+        iframe.teardown();
+        iframe = null;
+      }
+    });
 
     setup(function() {
       globalObject = {};
@@ -292,5 +299,33 @@ suite('Core', function() {
       assert.equal(globalObject.mouseX, 50);
       assert.isUndefined(logMsg);
     });
+
+    test('instance preload is independent of window', function() {
+      // callback for p5 instance mode.
+      // It does not define a preload.
+      // This tests that we don't call the global preload accidentally.
+      function cb(s) {
+        s.setup = function() {
+          window.afterSetup();
+        };
+      }
+      return new Promise(function(resolve) {
+        iframe = createP5Iframe(
+          [
+            P5_SCRIPT_TAG,
+            '<script>',
+            'globalPreloads = 0;',
+            'function setup() { }',
+            'function preload() { window.globalPreloads++; }',
+            'new p5(' + cb.toString() + ');',
+            '</script>'
+          ].join('\n')
+        );
+        iframe.elt.contentWindow.afterSetup = resolve;
+      }).then(function() {
+        var win = iframe.elt.contentWindow;
+        assert.strictEqual(win.globalPreloads, 1);
+      });
+    });
   });
 });

test/unit/core/structure.js

@@ -258,7 +258,16 @@ suite('Structure', function() {
     });
   });
 
-  suite('p5.prototype.redraw', function() {
+  suite.only('p5.prototype.redraw', function() {
+    var iframe;
+
+    teardown(function() {
+      if (iframe) {
+        iframe.teardown();
+        iframe = null;
+      }
+    });
+
     test('resets the rendering matrix between frames', function() {
       return new Promise(function(resolve, reject) {
         myp5.draw = function() {
@@ -274,5 +283,33 @@ suite('Structure', function() {
         resolve();
       });
     });
+
+    test('instance redraw is independent of window', function() {
+      // callback for p5 instance mode.
+      // It does not call noLoop so redraw will be called many times.
+      // Redraw is not supposed to call window.draw even though no draw is defined in cb
+      function cb(s) {
+        s.setup = function() {
+          setTimeout(window.afterSetup, 1000);
+        };
+      }
+      return new Promise(function(resolve) {
+        iframe = createP5Iframe(
+          [
+            P5_SCRIPT_TAG,
+            '<script>',
+            'globalDraws = 0;',
+            'function setup() { noLoop(); }',
+            'function draw() { window.globalDraws++; }',
+            'new p5(' + cb.toString() + ');',
+            '</script>'
+          ].join('\n')
+        );
+        iframe.elt.contentWindow.afterSetup = resolve;
+      }).then(function() {
+        var win = iframe.elt.contentWindow;
+        assert.strictEqual(win.globalDraws, 1);
+      });
+    });
   });
 });