fix: Cryptic error message when "delay" value is a number

close #3

Author: urish

src/TestScenario.ts

@@ -3,7 +3,9 @@ import type { APIClient } from './APIClient.js';
 import type { EventManager } from './EventManager.js';
 
 export interface IScenarioCommand {
-  validate?(params: any): boolean;
+  /** Validates the input to the command. Throws an exception of the input is not valid */
+  validate?(params: any): void;
+
   run(scenario: TestScenario, client: APIClient, params: any): Promise<void>;
 }
 
@@ -61,9 +63,12 @@ export class TestScenario {
       }
 
       for (const key of Object.keys(step)) {
-        if (!validStepKeys.includes(key) && !Object.keys(this.handlers).includes(key)) {
+        const handler = this.handlers[key];
+        if (!validStepKeys.includes(key) && !handler) {
           throw new Error(`Invalid scenario step key: ${key}`);
         }
+
+        handler?.validate?.(step[key]);
       }
     }
   }

src/scenario/DelayCommand.ts

@@ -8,6 +8,17 @@ import { promiseAndResolver } from '../utils/promise.js';
 export class DelayCommand {
   constructor(readonly eventManager: EventManager) {}
 
+  validate(value: string) {
+    if (typeof value === 'number') {
+      throw new Error(
+        `Invalid delay value ${value}. The value must include units (e.g. ${value}ms)`,
+      );
+    }
+    if (typeof value !== 'string') {
+      throw new Error(`Delay value must be a string`);
+    }
+  }
+
   async run(scenario: TestScenario, client: APIClient, value: string) {
     const nanos = parseTime(value);
     const targetNanos = (client.lastNanos ?? 0) + nanos;