Resolves where the JUnit document is written: --junit=<path> (relative to the project root) when given a string, else <output>/junit.xml.

import type { ReporterContext } from './types.ts';

const context = { projectRoot: '/repo', output: 'tmp', junit: true } as ReporterContext;
outputPath(context); // '/repo/tmp/junit.xml'
outputPath({ ...context, junit: 'reports/junit.xml' }); // '/repo/reports/junit.xml'