refactor: strictly typed

test/stub/mockfs.ts

@@ -21,7 +21,7 @@ export function mock (options: { [path: string]: (string | fileDescriptor) }) {
     return file.content
   }
 
-  fs.exists = async function (path) {
+  fs.exists = async function (path: string) {
     console.log('mock fs exists called', path)
     return !!files[path]
   }

test/stub/render.ts

@@ -12,7 +12,7 @@ export const ctx = {
   posts: [{ category: 'foo' }, { category: 'bar' }]
 }
 
-export async function test (src, dst) {
+export async function test (src: string, dst: string) {
   const html = await liquid.parseAndRender(src, ctx)
   return expect(html).to.equal(dst)
 }