diff --git a/web/unit_tests/cases/attachmentAPI.js b/web/unit_tests/cases/attachmentAPI.js
index e4bc9cd498..488761b932 100644
--- a/web/unit_tests/cases/attachmentAPI.js
+++ b/web/unit_tests/cases/attachmentAPI.js
@@ -3,26 +3,23 @@ var assert = chai.assert;
 describe('Attachment API', function() {
   this.timeout(testconfig.timeouts.standard);
 
-  before(function(done) {
+  before(function() {
     assert.isFalse(com.keyman.karma.DEVICE_DETECT_FAILURE, "Cannot run due to device detection failure.");
     fixture.setBase('fixtures');
 
     this.timeout(testconfig.timeouts.scriptLoad * 3);
-    setupKMW({ attachType:'manual' }, function() {
-      loadKeyboardFromJSON("/keyboards/lao_2008_basic.json", function() {
-        // Sequential so we don't have to worry about race conditions and such
-        // to signal completion with done().
-
-        loadKeyboardFromJSON("/keyboards/khmer_angkor.json", function() {
-          keyman.setActiveKeyboard("lao_2008_basic");
-          done();
-        }, testconfig.timeouts.scriptLoad);
-      }, testconfig.timeouts.scriptLoad);
-    }, testconfig.timeouts.scriptLoad);
+    return setupKMW({ attachType:'manual' }, testconfig.timeouts.scriptLoad).then(() => {
+      const kbd1 = loadKeyboardFromJSON("/keyboards/lao_2008_basic.json", testconfig.timeouts.scriptLoad, { passive: true });
+      const kbd2 = loadKeyboardFromJSON("/keyboards/khmer_angkor.json",   testconfig.timeouts.scriptLoad, { passive: true });
+      return Promise.all([kbd1, kbd2]).then(() => {
+        return keyman.setActiveKeyboard("lao_2008_basic");
+      });
+    });
   });
 
   after(function() {
     keyman.removeKeyboards('lao_2008_basic');
+    keyman.removeKeyboards('khmer_angkor');
     teardownKMW();
   });
 
@@ -193,11 +190,11 @@ Modernizr.on('touchevents', function(result) {
 
       this.timeout(testconfig.timeouts.standard);
 
-      before(function(done) {
+      before(function() {
         this.timeout(testconfig.timeouts.scriptLoad);
 
         fixture.setBase('fixtures');
-        setupKMW({ attachType:'auto' }, done, testconfig.timeouts.scriptLoad);
+        return setupKMW({ attachType:'auto' }, testconfig.timeouts.scriptLoad);
       });
 
       beforeEach(function() {
@@ -261,11 +258,11 @@ Modernizr.on('touchevents', function(result) {
 
       this.timeout(testconfig.timeouts.standard);
 
-      before(function(done) {
+      before(function() {
         this.timeout(testconfig.timeouts.scriptLoad);
 
         fixture.setBase('fixtures');
-        setupKMW({ attachType:'auto' }, done, testconfig.timeouts.scriptLoad);
+        return setupKMW({ attachType:'auto' }, testconfig.timeouts.scriptLoad);
       });
 
       beforeEach(function() {
diff --git a/web/unit_tests/cases/basics.js b/web/unit_tests/cases/basics.js
index 621161aa9b..c3d77779bb 100644
--- a/web/unit_tests/cases/basics.js
+++ b/web/unit_tests/cases/basics.js
@@ -8,12 +8,12 @@ describe('Basic KeymanWeb', function() {
     assert.isFalse(com.keyman.karma.DEVICE_DETECT_FAILURE, "Cannot run due to device detection failure.");
   })
 
-  beforeEach(function(done) {
+  beforeEach(function() {
     this.timeout(testconfig.timeouts.scriptLoad);
 
     fixture.setBase('fixtures');
     fixture.load("singleInput.html");
-    setupKMW(null, done, testconfig.timeouts.scriptLoad);
+    return setupKMW(null, testconfig.timeouts.scriptLoad);
   });
 
   afterEach(function() {
@@ -37,13 +37,13 @@ Modernizr.on('touchevents', function(result) {
     describe('Basic Toggle UI', function() {
       this.timeout(testconfig.timeouts.scriptLoad);
 
-      beforeEach(function(done) {
+      beforeEach(function() {
         this.timeout(testconfig.timeouts.uiLoad);
         fixture.setBase('fixtures');
         fixture.load('singleInput.html');
 
-        // Sequentially loads two scripts, so 2x timeout.
-        setupKMW('toggle', done, testconfig.timeouts.uiLoad, function() { return keyman.ui.initialized; });
+        // Loads two scripts in parallel, but just in case, 2x timeout.
+        return setupKMW('toggle', testconfig.timeouts.uiLoad);
       });
 
       afterEach(function() {
@@ -71,13 +71,13 @@ Modernizr.on('touchevents', function(result) {
 
     describe('Basic Button UI', function() {
 
-      beforeEach(function(done) {
+      beforeEach(function() {
         this.timeout(testconfig.timeouts.uiLoad);
         fixture.setBase('fixtures');
         fixture.load('singleInput.html');
 
-        // Sequentially loads two scripts, so 2x timeout.
-        setupKMW('button', done, testconfig.timeouts.uiLoad, function() { return keyman.ui.init; });
+        // Loads two scripts in parallel, but just in case, 2x timeout.
+        return setupKMW('button', testconfig.timeouts.uiLoad);
       });
 
       afterEach(function() {
@@ -92,13 +92,13 @@ Modernizr.on('touchevents', function(result) {
 
     describe('Basic Float UI', function() {
 
-      beforeEach(function(done) {
+      beforeEach(function() {
         this.timeout(testconfig.timeouts.uiLoad);
         fixture.setBase('fixtures');
         fixture.load('singleInput.html');
 
-        // Sequentially loads two scripts, so 2x timeout.
-        setupKMW('float', done, testconfig.timeouts.uiLoad, function() { return keyman.ui.initialized; });
+        // Loads two scripts in parallel, but just in case, 2x timeout.
+        return setupKMW('float', testconfig.timeouts.uiLoad);
       });
 
       afterEach(function() {
@@ -126,12 +126,13 @@ Modernizr.on('touchevents', function(result) {
 
     describe('Basic Toolbar UI', function() {
 
-      beforeEach(function(done) {
+      beforeEach(function() {
         this.timeout(testconfig.timeouts.uiLoad);
         fixture.setBase('fixtures');
         fixture.load('singleInput.html');
 
-        setupKMW('toolbar', done, testconfig.timeouts.uiLoad, function() { return keyman.ui.init; });
+        // Loads two scripts in parallel, but just in case, 2x timeout.
+        return setupKMW('toolbar', testconfig.timeouts.uiLoad);
       });
 
       afterEach(function() {
diff --git a/web/unit_tests/cases/engine.js b/web/unit_tests/cases/engine.js
index dbc8e69a32..87caf0b454 100644
--- a/web/unit_tests/cases/engine.js
+++ b/web/unit_tests/cases/engine.js
@@ -3,9 +3,9 @@ var assert = chai.assert;
 describe('Engine - Browser Interactions', function() {
   this.timeout(testconfig.timeouts.scriptLoad);
 
-  before(function(done) {
+  before(function() {
     fixture.setBase('fixtures');
-    setupKMW(null, done, testconfig.timeouts.scriptLoad);
+    return setupKMW(null, testconfig.timeouts.scriptLoad);
   });
 
   beforeEach(function(done) {
@@ -24,26 +24,8 @@ describe('Engine - Browser Interactions', function() {
     fixture.cleanup();
   });
 
-  describe('Keyboard Loading', function() {
-    it('Local', function(done) {
-      this.timeout(testconfig.timeouts.scriptLoad);
-
-      var test_callback = function() {
-        assert.isNotNull(keyman.getKeyboard("lao_2008_basic", "lo"), "Keyboard stub was not registered!");
-        assert.equal(keyman.getActiveKeyboard(), "Keyboard_lao_2008_basic", "Keyboard not set automatically!");
-        keyman.removeKeyboards('lao_2008_basic');
-        assert.equal(keyman.getActiveKeyboard(), '', "Keyboard not removed correctly!");
-        done();
-      }
-
-      loadKeyboardFromJSON("/keyboards/lao_2008_basic.json", test_callback, testconfig.timeouts.scriptLoad, {passive: true});
-    });
-  });
-
   describe('RegisterStub', function() {
-    it.skip('RegisterStub on same keyboard twice', function(done) {
-      // mcdurdin: skipping this test for now as it is sporadically failing and have not been able to trace source of issue
-      // see https://github.com/keymanapp/keyman/issues/5799
+    it('RegisterStub on same keyboard twice', function() {
       this.timeout(testconfig.timeouts.scriptLoad);
 
       var test_callback = function() {
@@ -51,10 +33,10 @@ describe('Engine - Browser Interactions', function() {
         assert.equal(keyman.getActiveKeyboard(), "Keyboard_lao_2008_basic", "Keyboard not set automatically!");
         keyman.removeKeyboards('lao_2008_basic');
         assert.equal(keyman.getActiveKeyboard(), '', "Keyboard not removed correctly!");
-        done();
       }
 
-      loadKeyboardFromJSON("/keyboards/lao_2008_basic.json", test_callback, testconfig.timeouts.scriptLoad, {passive: true});
+      let finalPromise = loadKeyboardFromJSON("/keyboards/lao_2008_basic.json", testconfig.timeouts.scriptLoad)
+        .then(test_callback);
 
       var stub = {
         'KI': 'Keyboard_lao_2008_basic',
@@ -64,7 +46,7 @@ describe('Engine - Browser Interactions', function() {
         'KF': 'resources/keyboards/lao_2008_basic.js'
       };
       assert.equal(com.keyman.text.KeyboardInterface.prototype.registerStub(stub), 1, "Registering existing keyboard should return 1!");
-      done();
+      return finalPromise;
     });
 
   });
@@ -72,8 +54,8 @@ describe('Engine - Browser Interactions', function() {
   describe('Variable Stores', function() {
     this.timeout(testconfig.timeouts.scriptLoad + testconfig.timeouts.standard);
 
-    beforeEach(function(done) {
-      loadKeyboardFromJSON("/keyboards/options_with_save.json", done, testconfig.timeouts.scriptLoad);
+    beforeEach(function() {
+      return loadKeyboardFromJSON("/keyboards/options_with_save.json", testconfig.timeouts.scriptLoad);
     });
 
     after(function() {
@@ -110,9 +92,10 @@ describe('Engine - Browser Interactions', function() {
           done();
         }
 
-        loadKeyboardFromJSON("/keyboards/options_with_save.json", function() {
-          keyman.setActiveKeyboard(keyboardID, 'en').then(remainderOfTest);
-        }, testconfig.timeouts.scriptLoad);
+        return loadKeyboardFromJSON("/keyboards/options_with_save.json", testconfig.timeouts.scriptLoad)
+          .then(() => {
+            return keyman.setActiveKeyboard(keyboardID, 'en');
+          }).then(remainderOfTest);
       });
     });
 
@@ -144,9 +127,9 @@ describe('Engine - Browser Interactions', function() {
   describe('Integrated Simulation Checks', function() {
     this.timeout(testconfig.timeouts.standard);
 
-    before(function(done){
+    before(function() {
       this.timeout = testconfig.timeouts.scriptLoad;
-      loadKeyboardFromJSON("/keyboards/lao_2008_basic.json", done, testconfig.timeouts.scriptLoad);
+      return loadKeyboardFromJSON("/keyboards/lao_2008_basic.json", testconfig.timeouts.scriptLoad);
     });
 
     beforeEach(function() {
@@ -213,9 +196,9 @@ describe('Engine - Browser Interactions', function() {
 describe('Unmatched Final Groups', function() {
   this.timeout(testconfig.timeouts.scriptLoad);
 
-  before(function(done) {
+  before(function() {
     fixture.setBase('fixtures');
-    setupKMW(null, done, testconfig.timeouts.scriptLoad + testconfig.timeouts.eventDelay);
+    return setupKMW(null, testconfig.timeouts.scriptLoad + testconfig.timeouts.eventDelay);
   });
 
   beforeEach(function(done) {
@@ -240,3 +223,82 @@ describe('Unmatched Final Groups', function() {
     runKeyboardTestFromJSON('/engine_tests/ghp_enter.json', {usingOSK: true}, done, assert.equal, testconfig.timeouts.scriptLoad);
   });
 });
+
+// Kept separate to maintain an extra-clean setup for this test.
+describe('Engine - Browser Interactions', function() {
+  this.timeout(testconfig.timeouts.scriptLoad);
+
+  before(function() {
+    fixture.setBase('fixtures');
+  });
+
+  beforeEach(function() {
+    fixture.load("singleInput.html");
+    return setupKMW(null, testconfig.timeouts.scriptLoad);
+  });
+
+  afterEach(function() {
+    fixture.cleanup();
+    teardownKMW();
+  });
+
+  describe('Keyboard Loading', function() {
+    it('Local', function() {
+      this.timeout(testconfig.timeouts.scriptLoad);
+
+      var test_callback = function() {
+        assert.isNotNull(keyman.getKeyboard("lao_2008_basic", "lo"), "Keyboard stub was not registered!");
+        assert.equal(keyman.getActiveKeyboard(), "Keyboard_lao_2008_basic", "Keyboard not set automatically!");
+        keyman.removeKeyboards('lao_2008_basic');
+        assert.equal(keyman.getActiveKeyboard(), '', "Keyboard not removed correctly!");
+      }
+
+      return loadKeyboardFromJSON("/keyboards/lao_2008_basic.json", testconfig.timeouts.scriptLoad)
+        .then(test_callback);
+    });
+
+    it('Automatically sets first available keyboard', function() {
+      this.timeout(2 * testconfig.timeouts.scriptLoad);
+
+      var test_callback = function() {
+        assert.isNotNull(keyman.getKeyboard("lao_2008_basic", "lo"), "Keyboard stub was not registered!");
+        assert.equal(keyman.getActiveKeyboard(), "Keyboard_lao_2008_basic", "Keyboard not set automatically!");
+        keyman.removeKeyboards('lao_2008_basic');
+        assert.equal(keyman.getActiveKeyboard(), '', "Keyboard not removed correctly!");
+      }
+
+      return loadKeyboardFromJSON("/keyboards/lao_2008_basic.json", testconfig.timeouts.scriptLoad, {passive: true})
+        .then(() => {
+          // Because we're loading the keyboard 'passively', KMW's setActiveKeyboard function is auto-called
+          // on the stub-add.  That specific call (for first keyboard auto-activation) is outside of KMW's
+          // current Promise chain, so we can't _directly_ rely on a KMW Promise to test it.
+          return new Promise((resolve) => {
+            let hasResolved = false;
+            // So, we give KMW the time needed for auto-activation to happen, polling a bit actively so that we don't
+            // wait unnecessarily long after it occurs.
+            let absoluteTimer = window.setTimeout(() => {
+              if(!hasResolved) {
+                resolve();
+                hasResolved = true;
+              }
+
+              window.clearTimeout(intervalTimer);
+            }, testconfig.timeouts.scriptLoad);
+
+            let intervalTimer = window.setInterval(() => {
+              if(keyman.getActiveKeyboard() != '') {
+                window.clearTimeout(intervalTimer);
+                window.clearTimeout(absoluteTimer);
+
+                if(!hasResolved) {
+                  resolve();
+                  hasResolved = true;
+                }
+              }
+            }, 50);
+          });
+          // Once this delay-Promise resolves successfully (either way)...
+        }).then(test_callback);  // THEN we run our checks.
+    });
+  });
+});
\ No newline at end of file
diff --git a/web/unit_tests/cases/engine_chirality.js b/web/unit_tests/cases/engine_chirality.js
index 80ebcce0c3..fa186f8146 100644
--- a/web/unit_tests/cases/engine_chirality.js
+++ b/web/unit_tests/cases/engine_chirality.js
@@ -3,9 +3,9 @@ var assert = chai.assert;
 describe('Engine - Chirality', function() {
   this.timeout(testconfig.timeouts.scriptLoad);
 
-  before(function(done) {
+  before(function() {
     fixture.setBase('fixtures');
-    setupKMW(null, done, testconfig.timeouts.scriptLoad);
+    return setupKMW(null, testconfig.timeouts.scriptLoad);
   });
 
   beforeEach(function(done) {
diff --git a/web/unit_tests/cases/events.js b/web/unit_tests/cases/events.js
index f26003620e..e32ad27dfe 100644
--- a/web/unit_tests/cases/events.js
+++ b/web/unit_tests/cases/events.js
@@ -3,21 +3,16 @@ var assert = chai.assert;
 describe('Event Management', function() {
   this.timeout(testconfig.timeouts.standard);
 
-  before(function(done) {
+  before(function() {
     this.timeout(testconfig.timeouts.scriptLoad * 2);
     fixture.setBase('fixtures');
     fixture.load("eventTestConfig.html");
 
-    setupKMW(null, function() {
+    return setupKMW(null, testconfig.timeouts.scriptLoad).then(() => {
       // We use this keyboard since we only need minimal input functionality for these tests.
       // Smaller is better when dealing with net latency.
-      loadKeyboardFromJSON("/keyboards/test_simple_deadkeys.json", function() {
-        // Interestingly, when auto-testing there's a Safari bug that prevents
-        // this from being preserved after the first forced blur command below.
-        done();
-      }, testconfig.timeouts.scriptLoad);
-    }, testconfig.timeouts.scriptLoad);
-
+      return loadKeyboardFromJSON("/keyboards/test_simple_deadkeys.json", testconfig.timeouts.scriptLoad);
+    });
   });
 
   after(function() {
diff --git a/web/unit_tests/cases/text_selection.js b/web/unit_tests/cases/text_selection.js
index bc5f31ba92..33ad0061e4 100644
--- a/web/unit_tests/cases/text_selection.js
+++ b/web/unit_tests/cases/text_selection.js
@@ -76,19 +76,18 @@ describe('Text Selection', function() {
   // TODO: Add automated tests for editable DIV, designMode iframe
   for(var inputType of ['Input', 'TextArea']) {
     describe('Text Selection in '+inputType, function() {
-      before(function(done) {
+      before(function() {
         // These tests require use of KMW's device-detection functionality.
         assert.isFalse(com.keyman.karma.DEVICE_DETECT_FAILURE, "Cannot run due to device detection failure.");
         fixture.setBase('fixtures');
         fixture.load("single"+inputType+".html");
 
         this.timeout(testconfig.timeouts.scriptLoad*2);
-        setupKMW(null, function() {
-          loadKeyboardFromJSON("/keyboards/web_context_tests.json", function() {
-            keyman.setActiveKeyboard("web_context_tests");
-            done();
-          }, testconfig.timeouts.scriptLoad);
-        }, testconfig.timeouts.scriptLoad);
+        return setupKMW(null, testconfig.timeouts.scriptLoad).then(() => {
+          return loadKeyboardFromJSON("/keyboards/web_context_tests.json", testconfig.timeouts.scriptLoad).then(() => {
+            return keyman.setActiveKeyboard("web_context_tests");
+          });
+        });
       });
 
       after(function() {
diff --git a/web/unit_tests/test_utils.js b/web/unit_tests/test_utils.js
index 06e98bc316..b20a52773e 100644
--- a/web/unit_tests/test_utils.js
+++ b/web/unit_tests/test_utils.js
@@ -16,7 +16,7 @@ try {
 
 // Keyman test suite utility methods
 
-var setupKMW = function(kmwOptions, done, timeout, uiInitCheck) {
+var setupKMW = function(kmwOptions, timeout) {
   var ui;
 
   if(typeof(kmwOptions) == 'string' || typeof(kmwOptions) == 'undefined' || kmwOptions == null) {
@@ -33,8 +33,9 @@ var setupKMW = function(kmwOptions, done, timeout, uiInitCheck) {
     }
   }
 
-  var kmw = setupScript('source/keymanweb.js', done, timeout, uiInitCheck);
-  fixture.el.appendChild(kmw);
+  const kmwPromise = setupScript('source/keymanweb.js', timeout, (scriptEle) => {
+    fixture.el.appendChild(scriptEle);
+  });
 
   ui = kmwOptions.ui;
 
@@ -48,43 +49,68 @@ var setupKMW = function(kmwOptions, done, timeout, uiInitCheck) {
     kmwOptions.resources = '../../../../source';
   }
 
+  let uiPromise;
   if(ui) {
-    var ui = setupScript('source/kmwui' + ui + '.js');
-    fixture.el.appendChild(ui);
+    uiPromise = setupScript('source/kmwui' + ui + '.js', timeout, (scriptEle) => {
+      fixture.el.appendChild(scriptEle);
+    });
 
     kmwOptions.ui=ui;
   }
 
-  var initFunc = function() {
-    if(window['keyman']) {
-      window['keyman'].init(kmwOptions);
-    } else {
-      window.setTimeout(function() {
-        initFunc();
-      })
-    }
-  };
-
-  /* Keep this timeout short - if set too long, kmwinit's default initialization
-   * will kick in and prevent our settings from going through!
-   */
-  window.setTimeout(function() {
-    initFunc();
-  }, 5);
-}
-
-var setupScript = function(src, done, timeout, uiInitCheck) {
-  var Lscript = document.createElement('script');
-  Lscript.charset="UTF-8";        // KMEW-89
-  Lscript.type = 'text/javascript';
-  Lscript.async = false;
-  if(done) {
-    Lscript.onload = initTimer(done, timeout, uiInitCheck);
+  let compositePromise = kmwPromise;
+  if(uiPromise) {
+    compositePromise = Promise.all([kmwPromise, uiPromise]);
   }
 
-  Lscript.src = src;
+  return finalPromise = compositePromise.then(() => {
+    if(window['keyman']) {
+      return window['keyman'].init(kmwOptions);
+    } else {
+      return Promise.reject();
+    }
+  });
+}
 
-  return Lscript;
+/**
+ * Produces a script element tied to a Promise for its eventual load (or failure thereof).
+ *
+ * The script element is only available via callback due to implementation constraints.
+ *
+ * @param {*} src       The source script's (relative) path on the test server.
+ * @param {*} timeout
+ * @param {*} functor   A callback to handle the script element.
+ * @returns
+ */
+var setupScript = function(src, timeout, functor) {
+  return new Promise((resolve, reject) => {
+    const Lscript = document.createElement('script');
+    let hasResolved = false;
+    Lscript.charset="UTF-8";        // KMEW-89
+    Lscript.type = 'text/javascript';
+    Lscript.async = false;
+
+    const timer = window.setTimeout(() => {
+      reject("Script load attempt timed out.");
+    }, timeout);
+
+    Lscript.onload = Lscript.onreadystatechange = () => {
+      window.clearTimeout(timer);
+      if(!hasResolved && (Lscript.readyState === undefined || Lscript.readyState == "complete")) {
+        hasResolved = true;
+        resolve();
+      }
+    }
+
+    Lscript.onerror = (err) => {
+      window.clearTimeout(timer);
+      reject(err);
+    }
+
+    Lscript.src = src;
+
+    functor(Lscript);
+  });
 }
 
 var teardownKMW = function() {
@@ -113,110 +139,25 @@ var teardownKMW = function() {
   }
 }
 
-// Make sure the main script loads...
-var initTimer = function(done, timeout, uiInitCheck) {
-  var uiLoadDelay;
-  if(typeof(uiInitCheck) != 'function') {
-    uiInitCheck = function() { return true; };
-    uiLoadDelay = false;
-  } else {
-    uiLoadDelay = true;
-  }
-
-  // We need managed state for this.
-  var InitializationManager = function() {
-    this.killSwitch = false;
-
-    this.initCheckCallback = function() {
-      if(window['keyman'] && window['keyman'].initialized == 2 && uiInitCheck()) {
-        if(done) {
-          this.timer = window.setTimeout(function() {
-            // There can be some odd cross-interference with the UI modules and their initialization.
-            // We use a significant delay here to avoid said problems.
-            done();
-          }, uiLoadDelay ? 2000 : 0);
-        }
-      } else if(!this.killSwitch) {
-        this.timer = window.setTimeout(this.initCheckCallback, 50);
-      }
-    }.bind(this);
-
-    if(timeout) {
-      window.setTimeout(function() {
-        this.killSwitch = true;
-
-        if(this.timer) {
-          window.clearTimeout(this.timer);
-          this.timer = 0;
-        }
-      }.bind(this), timeout);
-    }
-  }
-
-  var im = new InitializationManager();
-  return im.initCheckCallback;
-};
-
-// Make sure the main script loads...
-var onScriptLoad = function(scriptURL, callback, timeout) {
-  var ScriptLoadObserver = function() {
-    this.target = document.createElement('a');
-    this.target.href = scriptURL;
-
-    if(timeout) {
-      this.timer = window.setTimeout(function() {
-        if(this.mo) {
-          this.mo.disconnect();
-        }
-      }.bind(this), timeout);
-    }
-
-    var moCallback = function(mutations) {
-      for(var i=0; i < mutations.length; i++) {
-        var mutation = mutations[i];
-        for(var j=0; j < mutation.addedNodes.length; j++) {
-          var child = mutation.addedNodes[j];
-          if(child instanceof HTMLScriptElement) {
-            if(child.src == this.target.href) {
-              child.onload = callback;
-            }
-          }
-        }
-      }
-    }
-
-    this.observe = function() {
-      var config = { childList: true, subtree: true };
-      this.mo = new MutationObserver(moCallback.bind(this));
-      this.mo.observe(document, config);
-    }
-  }
-
-  var slo = new ScriptLoadObserver();
-  slo.observe();
-};
-
-var loadKeyboardStub = function(stub, callback, timeout, params) {
+var loadKeyboardStub = function(stub, timeout, params) {
   var kbdName = "Keyboard_" + stub.id;
 
   keyman.addKeyboards(stub);
   if(!params || !params.passive) {
-    keyman.setActiveKeyboard(kbdName, stub.languages.id);
-  }
-
-  if(keyman.getActiveKeyboard() != kbdName) {
-    onScriptLoad(stub.filename, function() {
-      callback();
-    }, timeout);
+    return keyman.setActiveKeyboard(kbdName, stub.languages.id);
+  } else if(keyman.getActiveKeyboard() != kbdName) {
+    return setupScript(stub.filename, timeout, (ele) => {
+      fixture.el.appendChild(ele);
+    });
   } else {
-    callback();
+    return Promise.resolve();
   }
 }
 
-var loadKeyboardFromJSON = function(jsonPath, callback, timeout) {
+var loadKeyboardFromJSON = function(jsonPath, timeout, params) {
   var stub = fixture.load(jsonPath, true);
 
-  loadKeyboardStub(stub, callback, timeout);
+  return loadKeyboardStub(stub, timeout, params);
 }
 
 function runLoadedKeyboardTest(testDef, device, usingOSK, assertCallback) {
@@ -234,11 +175,11 @@ function runKeyboardTestFromJSON(jsonPath, params, callback, assertCallback, tim
   let device = new com.keyman.Device();
   device.detect();
 
-  loadKeyboardStub(testSpec.keyboard, function() {
+  loadKeyboardStub(testSpec.keyboard, timeout).then(() => {
     runLoadedKeyboardTest(testSpec, device.coreSpec, params.usingOSK, assertCallback);
     keyman.removeKeyboards(testSpec.keyboard.id);
     callback();
-  }, timeout);
+  });
 }
 
 function retrieveAndReset(Pelem) {