feat: add useful error assertion message

lib/shared.ts

@@ -124,11 +124,15 @@ export async function waitForDeploymentRollout(
 
 export function throwWhen<T, Narrowed extends T>(
   condition: (arg: T) => arg is Narrowed,
+  message?: string,
 ): (arg: T) => Exclude<T, Narrowed>;
-export function throwWhen<T>(condition: (arg: T) => unknown): (arg: T) => T;
-export function throwWhen<T>(condition: (arg: T) => unknown) {
+export function throwWhen<T>(
+  condition: (arg: T) => unknown,
+  message?: string,
+): (arg: T) => T;
+export function throwWhen<T>(condition: (arg: T) => unknown, message?: string) {
   return (arg: T) => {
-    if (condition(arg)) throw new Error("Condition matched");
+    if (condition(arg)) throw new Error(message ?? "Condition matched");
     return arg;
   };
 }