Add NodeUnpublishVolume test for when the volume is missing

The spec mandates that such cases should return NOT_FOUND responses [1].

The mock driver already implements the right behavior.

[1] https://github.com/container-storage-interface/spec/blob/4731db0e0bc53238b93850f43ab05d9355df0fd9/spec.md#nodeunpublishvolume-errors

Author: timoreimann

pkg/sanity/node.go

@@ -241,6 +241,21 @@ var _ = DescribeSanity("Node Service", func(sc *TestContext) {
 			Expect(ok).To(BeTrue())
 			Expect(serverError.Code()).To(Equal(codes.InvalidArgument))
 		})
+
+		It("should fail when the volume is missing", func() {
+
+			_, err := c.NodeUnpublishVolume(
+				context.Background(),
+				&csi.NodeUnpublishVolumeRequest{
+					VolumeId:   sc.Config.IDGen.GenerateUniqueValidVolumeID(),
+					TargetPath: sc.StagingPath,
+				})
+			Expect(err).To(HaveOccurred())
+
+			serverError, ok := status.FromError(err)
+			Expect(ok).To(BeTrue())
+			Expect(serverError.Code()).To(Equal(codes.NotFound))
+		})
 	})
 
 	Describe("NodeStageVolume", func() {