Merge 399a4e7 into 78287c9

src/vaadin-date-picker-mixin.html

@@ -439,8 +439,11 @@
         this.__dispatchChange = true;
       }
       const inputValue = selectedDate && formatDate(Vaadin.DatePickerHelper._extractDateParts(selectedDate));
-      this.validate(inputValue);
-      this.value = this._formatISO(selectedDate);
+      const value = this._formatISO(selectedDate);
+      if (value !== this.value) {
+        this.validate(inputValue);
+        this.value = value;
+      }
       this.__userInputOccurred = false;
       this.__dispatchChange = false;
       this._focusedDate = selectedDate;

test/form-input.html

@@ -37,6 +37,12 @@
     </template>
   </test-fixture>
 
+  <test-fixture id="datepicker-required">
+    <template>
+      <vaadin-date-picker required></vaadin-date-picker>
+    </template>
+  </test-fixture>
+
   <test-fixture id="datepicker-in-form">
     <template>
       <iron-form>
@@ -218,6 +224,24 @@
       });
     });
 
+    describe('required', () => {
+      let datepicker;
+
+      beforeEach(done => {
+        datepicker = fixture('datepicker-required');
+        setTimeout(done);
+      });
+
+      it('should not be invalid without user interactions', () => {
+        expect(datepicker.invalid).to.be.false;
+      });
+
+      it('should be invalid after validate() if value is not set', () => {
+        datepicker.validate();
+        expect(datepicker.invalid).to.be.true;
+      });
+    });
+
     describe('using as a field in an iron-form', () => {
       var datepicker, ironForm;