select single element on cmd-click (#2087)

src/tests/regressionTests.test.tsx

@@ -50,6 +50,20 @@ const group = (elements: ExcalidrawElement[]) => {
   });
 };
 
+const assertSelectedElements = (...elements: ExcalidrawElement[]) => {
+  expect(
+    getSelectedElements().map((element) => {
+      return element.id;
+    }),
+  ).toEqual(expect.arrayContaining(elements.map((element) => element.id)));
+};
+
+const clearSelection = () => {
+  // @ts-ignore
+  h.app.clearSelection(null);
+  expect(getSelectedElements().length).toBe(0);
+};
+
 let altKey = false;
 let shiftKey = false;
 let ctrlKey = false;
@@ -191,8 +205,7 @@ class Pointer {
     /** if multiple elements supplied, they're shift-selected */
     elements: ExcalidrawElement | ExcalidrawElement[],
   ) {
-    // @ts-ignore
-    h.app.clearSelection(null);
+    clearSelection();
     withModifierKeys({ shift: true }, () => {
       elements = Array.isArray(elements) ? elements : [elements];
       elements.forEach((element) => {
@@ -1649,6 +1662,40 @@ describe("regression tests", () => {
     expect(h.state.selectedGroupIds).toEqual(selectedGroupIds_prev);
     expect(getSelectedElements()).toEqual(selectedElements_prev);
   });
+
+  it("Cmd/Ctrl-click exclusively select element under pointer", () => {
+    const rect1 = createElement("rectangle", { x: 0 });
+    const rect2 = createElement("rectangle", { x: 30 });
+
+    group([rect1, rect2]);
+    assertSelectedElements(rect1, rect2);
+
+    withModifierKeys({ ctrl: true }, () => {
+      mouse.clickOn(rect1);
+    });
+    assertSelectedElements(rect1);
+
+    clearSelection();
+    withModifierKeys({ ctrl: true }, () => {
+      mouse.clickOn(rect1);
+    });
+    assertSelectedElements(rect1);
+
+    const rect3 = createElement("rectangle", { x: 60 });
+    group([rect1, rect3]);
+    assertSelectedElements(rect1, rect2, rect3);
+
+    withModifierKeys({ ctrl: true }, () => {
+      mouse.clickOn(rect1);
+    });
+    assertSelectedElements(rect1);
+
+    clearSelection();
+    withModifierKeys({ ctrl: true }, () => {
+      mouse.clickOn(rect3);
+    });
+    assertSelectedElements(rect3);
+  });
 });
 
 it(