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TestBed.overrideComponent and TestBed.overrideModule don't seem to work with karma, webpack builder (builderMode: browser) and aot enabled. Changing any of these settings, so builderMode: application or disabling aot "fixes" the problem. The same issue was reported here #30017 but i guess it was only fixed for esbuild? Is there any workaround for this? or can it be fixed for angular20?

Minimal Reproduction

Create a simple valid component, turn on AOT for Karma, and make a test where you use TestBed.overrideComponent to reset metadata. You don't even need to specify an actual override in the second parameter to trigger the issue: TestBed.overrideComponent(YourComponent, {}) triggers the failure.

builderMode: browser needs to be set

Exception or Error

Error: App class doesn't have @Component decorator or is missing metadata.
            at invalidTypeError (node_modules/@angular/core/fesm2022/testing.mjs:1661:12)
            at forEach (node_modules/@angular/core/fesm2022/testing.mjs:1084:23)
            at asyncGeneratorStep (node_modules/@babel/runtime/helpers/esm/asyncToGenerator.js:3:1)
            at apply (node_modules/@babel/runtime/helpers/esm/asyncToGenerator.js:17:1)
            at _ZoneDelegate.invoke (node_modules/zone.js/fesm2015/zone.js:398:28)
            at ProxyZoneSpec.onInvoke (node_modules/zone.js/fesm2015/zone-testing.js:2132:39)

Your Environment

_                      _                 ____ _     ___
    / \   _ __   __ _ _   _| | __ _ _ __     / ___| |   |_ _|
   / △ \ | '_ \ / _` | | | | |/ _` | '__|   | |   | |    | |
  / ___ \| | | | (_| | |_| | | (_| | |      | |___| |___ | |
 /_/   \_\_| |_|\__, |\__,_|_|\__,_|_|       \____|_____|___|
                |___/
    


Angular CLI: 20.3.18
Node: 22.22.0
Package Manager: npm 10.9.4
OS: win32 x64


Angular: 20.3.17
... common, compiler, compiler-cli, core, forms
... platform-browser, router

Package                         Version
---------------------------------------
@angular-devkit/architect       0.2003.18
@angular-devkit/build-angular   20.3.16
@angular-devkit/core            20.3.18
@angular-devkit/schematics      20.3.18
@angular/build                  20.3.18
@angular/cli                    20.3.18
@schematics/angular             20.3.18
rxjs                            7.8.2
typescript                      5.9.3
zone.js                         0.15.1

Anything else relevant?

No response

Activity

alan-agius4
added
area: @angular-devkit/build-angular

devkit/build-angular:karma

type: bug/fix

freq1: lowOnly reported by a handful of users who observe it rarelyOnly reported by a handful of users who observe it rarely

severity3: broken
on Mar 2, 2026
alan-agius4
added the
Bug
issue type on Mar 2, 2026

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