Test my app with random errors

When building apps, you should test how your app handles API errors. Dev Proxy allows you to simulate errors on any API that you use in your app using the GenericRandomErrorPlugin.

Simulate errors on any API

To start, enable the GenericRandomErrorPlugin in your configuration file.

{
  "$schema": "https://raw.githubusercontent.com/microsoft/dev-proxy/main/schemas/v0.20.0/rc.schema.json",
  "plugins": [
    {
      "name": "GenericRandomErrorPlugin",
      "enabled": true,
      "pluginPath": "~appFolder/plugins/dev-proxy-plugins.dll",
      "configSection": "errorsContosoApi",
      "urlsToWatch": [
        "https://api.contoso.com/*"
      ]
    }
  ]
}

Tip

Because each API is different, you typically configure an instance of the GenericRandomErrorPlugin for each API you want to simulate errors on. To make it easier to manage the configuration, name the configSection after the API you want to simulate errors on. Additionally, specify the URLs that you want to simulate errors on in the urlsToWatch property with the plugin. This will make it easier to manage the configuration and reuse it in the future.

Next, configure the plugin to use a file that contains the errors you want to simulate.

{
  "errorsContosoApi": {
    "errorsFile": "errors-contoso-api.json"
  }
}

Finally, in the errors file, define the list of error responses that you want to simulate. For example, to simulate a 500 error with a custom JSON response, use the following configuration:

{
  "$schema": "https://raw.githubusercontent.com/microsoft/dev-proxy/main/schemas/v0.20.0/genericrandomerrorplugin.schema.json",
  "errors": [
    {
      "request": {
        "url": "https://api.contoso.com/*"
      },
      "responses": [
        {
          "statusCode": 500,
          "headers": [
            {
              "name": "content-type",
              "value": "application/json; charset=utf-8"
            }
          ],
          "body": {
            "code": "InternalServerError",
            "message": "Something went wrong"
          }
        }
      ]
    }
  ]
}

You can define as many error responses as you need.

Start Dev Proxy with your configuration file and use your app to see how it handles the errors. For each matching request, Dev Proxy determines whether to simulate an error or pass the request through to the original API using the configured failure rate. When Dev Proxy simulates an error, it uses a random error from the array of error responses you defined in the configuration file.

Temporarily disable mocks

If you use mocks in your configuration file, you can temporarily disable them by using the --no-mocks option.

devproxy --no-mocks

Next step

Learn more about the GenericRandomErrorPlugin.

GenericRandomErrorPlugin