Testing API and parsing error

[cdietrich]

we use the testing api of langium to test our semantic validations.
in order to make sure we have created a wrapper like this

validationHelperNoParsingErrors(....)
const result = call original one....
expectNoIssues(result, {
    severity: DiagnosticSeverity.Error,
    data: {
      code: "parsing-error",
    },
  })
  return result

i wonder if this could be an option for langium itself.

e.g.

export function validationHelper<T extends AstNode = AstNode>(services: LangiumCoreServices): (input: string, options?: ParseHelperOptions & {failOnParseErrors?: true}) => Promise<ValidationResult<T>> {
    const parse = parseHelper<T>(services);
    return async (input, options) => {
        const document = await parse(input, {
            ...(options ?? {}),
            validation: true
        });
        const result = {
            document,
            diagnostics: document.diagnostics ?? [],
            dispose: () => clearDocuments(services, [document])
        };
        if (options?.failOnParseErrors) {
            expectNoIssues(result, {
                severity: DiagnosticSeverity.Error,
                data: {
                    code: 'parsing-error',
                },
            });}
        return result;
    };
}

#1699