Angular 6 unit testing component with DomSanitizer dependency

As a workaround, try add sanitize: () => 'safeString',

...
useValue: {
  sanitize: () => 'safeString',
  bypassSecurityTrustHtml: () => 'safeString'
}
...

If you want to preserve the value, use:

{
  provide: DomSanitizer,
  useValue: {
    sanitize: (ctx: any, val: string) => val,
    bypassSecurityTrustResourceUrl: (val: string) => val,
  },
}