Encode input as JSON

Ref #4

harness/lib/suites/block-test.js

@@ -5,7 +5,10 @@ describe('block', function () {
   const { parse, tests } = this.parent.ctx
   const blockTests = tests.find((it) => it.type === 'dir' && it.name === 'block').entries
   makeTests(blockTests, async function ({ input, inputPath, expected, expectedWithoutLocations }) {
-    const actual = await parse(input)
+    const actual = await parse({
+      contents: input,
+      path: inputPath,
+    })
     if (expected == null) {
       // Q: can we write data to expect file automatically?
       // TODO only output expected if environment variable is set