Fix close button on add to cart confirm modal (#3114)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: cp-at-mit

frontend/public/src/components/CourseProductDetailEnroll.js

@@ -292,7 +292,10 @@ export class CourseProductDetailEnroll extends React.Component<
             <strong>{course && course.title}</strong> added to your cart.
           </div>
           <div className="float-container">
-            <button className="btn btn-gradient-white-to-blue btn-secondary close-dialog-btn">
+            <button
+              className="btn btn-gradient-white-to-blue btn-secondary close-dialog-btn"
+              onClick={() => this.toggleCartConfirmationDialogVisibility()}
+            >
               Close
             </button>
             <button

frontend/public/src/components/CourseProductDetailEnroll_test.js

@@ -995,4 +995,47 @@ describe("CourseProductDetailEnrollShallowRender", () => {
       }
     })
   })
+
+  it("closes add-to-cart confirmation dialog when Close button is clicked", async () => {
+    courseRun["products"] = [
+      {
+        id:    1,
+        price: 10
+      }
+    ]
+    course.next_run_id = courseRun.id
+    course.courseruns = [courseRun]
+
+    const { inner } = await renderPage(
+      {
+        entities: {
+          courses: [course]
+        },
+        queries: {
+          courses: {
+            isPending: false,
+            status:    200
+          }
+        }
+      },
+      { courseId: course.id }
+    )
+
+    inner.setState({ addedToCartDialogVisibility: true })
+    inner.update()
+
+    const modal = inner.find(".added-to-cart-modal")
+    assert.isTrue(modal.exists())
+    assert.isTrue(modal.prop("isOpen"))
+
+    const closeButton = modal.find(".close-dialog-btn")
+    assert.isTrue(closeButton.exists())
+
+    await closeButton.prop("onClick")()
+    inner.update()
+
+    const updatedModal = inner.find(".added-to-cart-modal")
+    assert.isFalse(updatedModal.prop("isOpen"))
+    assert.isFalse(inner.state("addedToCartDialogVisibility"))
+  })
 })