fix(test): properly clean input field (#860)

Author: aslushnikov

docs/api.md

@@ -1012,6 +1012,8 @@ const fs = require('fs');
 This method focuses the element and triggers an `input` event after filling.
 If there's no text `<input>`, `<textarea>` or `[contenteditable]` element matching `selector`, the method throws an error.
 
+> **NOTE** Pass empty string as a value to clear the input field.
+
 Shortcut for [page.mainFrame().fill()](#framefillselector-value)
 
 #### page.focus(selector, options)

src/dom.ts

@@ -414,7 +414,10 @@ export class ElementHandle<T extends Node = Node> extends js.JSHandle<T> {
     }, value);
     if (error)
       throw new Error(error);
-    await this._page.keyboard.sendCharacters(value);
+    if (value)
+      await this._page.keyboard.sendCharacters(value);
+    else
+      await this._page.keyboard.press('Delete');
   }
 
   async setInputFiles(...files: (string | types.FilePayload)[]) {