MultiCombobox: Fix select all when only a single option is available (#109910)

* Fix condition

* Add tests

packages/grafana-ui/src/components/Combobox/ComboboxList.tsx

@@ -67,7 +67,7 @@ export const ComboboxList = <T extends string | number>({
     [selectedItems]
   );
 
-  const allItemsSelected = enableAllOption && selectedItems.length === options.length - 1;
+  const allItemsSelected = enableAllOption && options.length > 1 && selectedItems.length === options.length - 1;
 
   return (
     <ScrollContainer showScrollIndicators maxHeight="inherit" ref={scrollRef} padding={0.5}>
@@ -142,6 +142,7 @@ export const ComboboxList = <T extends string | number>({
                         onClick={(e) => {
                           e.stopPropagation();
                         }}
+                        data-testid={`${itemId}-checkbox`}
                       />
                     )}
                   </div>

packages/grafana-ui/src/components/Combobox/MultiCombobox.test.tsx

@@ -281,6 +281,25 @@ describe('MultiCombobox', () => {
       await user.type(input, 'b');
       expect(screen.getByText('A')).toBeInTheDocument();
     });
+
+    it('should not render All when only one option is available and enableAll is true', async () => {
+      const options = [{ label: 'A', value: 'a' }];
+      render(<MultiCombobox width={200} options={options} onChange={jest.fn()} enableAllOption />);
+      const input = screen.getByRole('combobox');
+      await user.click(input);
+      expect(screen.queryByRole('option', { name: 'All' })).not.toBeInTheDocument();
+    });
+
+    it('should not select option when only one option is available and enableAll is true', async () => {
+      const options = [{ label: 'A', value: 'a' }];
+      render(<MultiCombobox width={200} options={options} onChange={jest.fn()} enableAllOption />);
+      const input = screen.getByRole('combobox');
+      await user.click(input);
+
+      const checkbox = screen.getByTestId(`combobox-option-${options[0].value}-checkbox`);
+      expect(checkbox).toBeInTheDocument();
+      expect(checkbox).not.toBeChecked();
+    });
   });
 
   describe('async', () => {