[bugfix] Tabs: incorrect line position in some cases (#3961)

test/utils/dom.ts

@@ -0,0 +1,48 @@
+import { trigger } from './event';
+
+function mockHTMLElementOffset() {
+  Object.defineProperties(HTMLElement.prototype, {
+    offsetParent: {
+      get() {
+        return this.parentNode || {};
+      }
+    },
+    offsetLeft: {
+      get() {
+        return parseFloat(window.getComputedStyle(this).marginLeft) || 0;
+      }
+    },
+    offsetTop: {
+      get() {
+        return parseFloat(window.getComputedStyle(this).marginTop) || 0;
+      }
+    },
+    offsetHeight: {
+      get() {
+        return parseFloat(window.getComputedStyle(this).height) || 0;
+      }
+    },
+    offsetWidth: {
+      get() {
+        return parseFloat(window.getComputedStyle(this).width) || 0;
+      }
+    }
+  });
+}
+
+mockHTMLElementOffset();
+
+export function mockGetBoundingClientRect(rect: ClientRect | DOMRect): Function {
+  const originMethod = Element.prototype.getBoundingClientRect;
+
+  Element.prototype.getBoundingClientRect = <any>jest.fn(() => rect);
+
+  return function () {
+    Element.prototype.getBoundingClientRect = originMethod;
+  };
+}
+
+export function mockScrollTop(value: number) {
+  Object.defineProperty(window, 'scrollTop', { value, writable: true });
+  trigger(window, 'scroll');
+}