[Autocomplete] Change behavior of mouseDown event and add new test case

The text box inside Autocomplete component responds to click event.
If the text box is empty it will toggle the list box.
If the text box is not empty it will only open the list box.

packages/material-ui-lab/src/Autocomplete/Autocomplete.test.js

@@ -1611,7 +1611,7 @@ describe('<Autocomplete />', () => {
       expect(handleChange.args[1][2]).to.equal('mouse');
     });
 
-    it('should open list box even if the input contains an option value', () => {
+    it('should mantain list box open clicking on input when it is not empty', () => {
       const handleChange = spy();
       const { queryByRole, getByRole, getAllByRole } = render(
         <Autocomplete
@@ -1622,12 +1622,33 @@ describe('<Autocomplete />', () => {
       );
       const textbox = getByRole('textbox');
       expect(queryByRole('presentation')).to.equal(null);
-      fireEvent.mouseDown(textbox);
+      fireEvent.mouseDown(textbox); // Open listbox
       expect(queryByRole('presentation')).to.not.equal(null);
       const options = getAllByRole('option');
       fireEvent.click(options[0]);
       expect(queryByRole('presentation')).to.equal(null);
-      fireEvent.mouseDown(textbox);
+      fireEvent.mouseDown(textbox); // Open listbox
+      expect(queryByRole('presentation')).to.not.equal(null);
+      fireEvent.mouseDown(textbox); // Remain open listbox
+      expect(queryByRole('presentation')).to.not.equal(null);
+    });
+
+    it('should toggle list box when input is empty', () => {
+      const handleChange = spy();
+      const { queryByRole, getByRole } = render(
+        <Autocomplete
+          onHighlightChange={handleChange}
+          options={['one']}
+          renderInput={(params) => <TextField {...params} />}
+        />,
+      );
+      const textbox = getByRole('textbox');
+      expect(queryByRole('presentation')).to.equal(null);
+      fireEvent.mouseDown(textbox); // Open listbox
+      expect(queryByRole('presentation')).to.not.equal(null);
+      fireEvent.mouseDown(textbox); // close listbox
+      expect(queryByRole('presentation')).to.equal(null);
+      fireEvent.mouseDown(textbox); // open listbox
       expect(queryByRole('presentation')).to.not.equal(null);
     });
   });

packages/material-ui-lab/src/useAutocomplete/useAutocomplete.js

@@ -860,7 +860,9 @@ export default function useAutocomplete(props) {
   };
 
   const handleInputMouseDown = (event) => {
-    handlePopupIndicator(event);
+    if (inputValue === '' || !open) {
+      handlePopupIndicator(event);
+    }
   };
 
   let dirty = freeSolo && inputValue.length > 0;