Primary finding
Middleware test re-derives response in beforeEach but `res` is typed as the implementation return — silently breaks if middleware ever returns void/undefined
lowtest-gapmedium
- apps/web/middleware.test.ts:24-33
makeReq() casts a bare `{ nextUrl: new URL(...) }` to NextRequest. If middleware ever begins reading `req.headers`, `req.cookies`, `req.method`, etc., the cast will silently produce `undefined` accesses and the resulting NextResponse may be malformed, but the header assertions will still pass or throw a hard-to-debug TypeError. The comment block 'We import the module's SECURITY_HEADERS map via re-export rather than instantiating the full middleware function with mock NextRequest' is misleading — the test does in fact instantiate middleware with a stub NextRequest, not import a SECURITY_HEADERS map.
Recommendation
Either (a) export SECURITY_HEADERS as a const from the middleware module and assert against that map directly (matching the comment), or (b) update the comment to accurately describe the current stub-request approach. Also use NextRequest's actual constructor (`new NextRequest(new URL('https://...'))`) instead of the unsafe cast to catch breakages at the type level.