A test in https://github.com/angular/angular/blob/main/packages/compiler-cli/test/ngtsc/template_typecheck_spec.ts would be meaningful to verify the template is checked as expected;

@Component({
  template: `
    @let var = `Version: \`${check(version)}\``;
  `
})
export class Cmp {
  version = 'test'
  check(input: number): string {
    return String(input);
  }
}

Should report a type assignability error from string to number. That shows that the template's substitutions are type-checked as expected.