unit-test builder doesn't work with server

[robertIsaac]

Command

test

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

No response

Description

in a newly generated v20 app with server side rendering when changing the test runner to vitest as announced in the v20 blog fails to work

Minimal Reproduction

generate a new app using ssr option
run npm i vitest jsdom --save-dev
in angular.json change test to

"test": {
    "builder": "@angular/build:unit-test",
    "options": {
        "tsConfig": "tsconfig.spec.json",
        "buildTarget": "::development",
        "runner": "vitest"
    }
}

Exception or Error

ng test
NOTE: The "unit-test" builder is currently EXPERIMENTAL and not ready for production use.
An unhandled exception occurred: The "server" option is required when "outputMode" is set to "server".
See "/private/var/folders/lt/jrs1vjm137nbc1xvctmzl7v40000gn/T/ng-sJrdPA/angular-errors.log" for further details.

Your Environment

Angular CLI: 20.0.0
Node: 22.14.0
Package Manager: npm 11.4.1
OS: darwin arm64

Angular: 20.0.0
... build, cli, common, compiler, compiler-cli, core, forms
... platform-browser, platform-server, router, ssr

Package                      Version
------------------------------------------------------
@angular-devkit/architect    0.2000.0
@angular-devkit/core         20.0.0
@angular-devkit/schematics   20.0.0
@schematics/angular          20.0.0
rxjs                         7.8.2
typescript                   5.8.3
zone.js                      0.15.1

Anything else relevant?

No response