try breaking asserts out into separate test functions

addon/components/tether-dialog.js

@@ -39,7 +39,7 @@ export default ModalDialog.extend({
     this._super(...arguments);
 
     if (this.get('mouseleaveToClose')) {
-      this._eventListenerNameSpace = `ember-modal-dialog.${this._mouseLeaveEventId}`;
+      this._eventListenerNameSpace = `ember-modal-dialog.${this.elementId}`;
 
       Ember.$('.ember-modal-dialog').on(`mouseleave.${this._eventListenerNameSpace}`, (event) => {
         // DON'T close if the mouse is leaving the target and entering the target

tests/acceptance/tether-dialog-test.js

@@ -114,7 +114,7 @@ test('target - view', function(assert) {
   });
 });
 
-test('mouseleaveToClose', function(assert) {
+test('mouseleaveToClose functions with manual close button', function(assert) {
   const openSelector = '#targetedMouseleaveToClose';
   const dialogText = 'Target w/ mouseleaveToClose';
 
@@ -125,16 +125,24 @@ test('mouseleaveToClose', function(assert) {
     hasOverlay: false,
     tethered: true
   });
+});
+
+test('mouseleaveToClose closes when a mouseleave event occurs on the dialog', function(assert) {
+  const openSelector = '#targetedMouseleaveToClose';
+  const dialogText = 'Target w/ mouseleaveToClose';
 
-  click(openSelector)
-    .then(() => {
-      return assert.closesOnMouseleave(dialogSelector, dialogText);
-    })
-    .then(() => {
-      click(openSelector).then(() => {
-        assert.closesOnMouseleave(openSelector, dialogText);
-      });
-    });
+  click(openSelector).then(() => {
+    return assert.closesOnMouseleave(dialogSelector, dialogText);
+  });
+});
+
+test('mouseleaveToClose closes when a mouseleave event occurs on the element used to open', function(assert) {
+  const openSelector = '#targetedMouseleaveToClose';
+  const dialogText = 'Target w/ mouseleaveToClose';
+
+  click(openSelector).then(() => {
+    return assert.closesOnMouseleave(openSelector, dialogText);
+  });
 });
 
 test('subclassed modal', function(assert) {

tests/helpers/modal-asserts.js

@@ -42,7 +42,8 @@ export default function registerAssertHelpers() {
 
   assert.closesOnMouseleave = function(mouseLeaveSelector, dialogText) {
     const dialogContent = [dialogSelector, `:contains(${dialogText})`].join('');
-    return triggerEvent(dialogContent, 'mouseleave').then(() => {
+
+    return triggerEvent(mouseLeaveSelector, 'mouseleave').then(() => {
       this.isAbsent(dialogContent);
     });
   };