Add failing test for partial attribute override

Currently the default attributes are only set correctly when either none
or all attributes are handed to the component

tests/unit/components/add-contribution-test.js

@@ -18,7 +18,24 @@ module('Unit | Component | add-contribution', function(hooks) {
       assert.equal(component.get(a), null, `sets the ${a} property`);
     });
 
-    assert.ok(moment.isDate(component.attributes.date, 'sets the default date attribute'));
+    assert.ok(moment.isDate(component.attributes.date), 'sets the default date attribute');
     assert.ok(moment.isDate(component.date), 'sets the default date');
   });
+
+  test('override default attributes', function(assert) {
+    let component = this.owner.factoryFor('component:add-contribution').create({
+      attributes: { contributorId: '1' }
+    });
+
+    assert.equal(component.contributorId, '1', `overrides the default property`);
+
+    ['kind', 'amount', 'description', 'url', 'details'].forEach(a => {
+      assert.equal(component.attributes[a], null, `sets the default ${a} attribute`);
+      assert.equal(component.get(a), null, `sets the ${a} property`);
+    });
+
+    assert.ok(moment.isDate(component.attributes.date), 'sets the default date attribute');
+    assert.ok(moment.isDate(component.date), 'sets the default date');
+  });
+
 });