improve test coverage for metamark exports

Author: aegatlin

test/metamark.exports.test.ts

@@ -4,7 +4,9 @@ import m from "../src/index";
 test("metamark exports", () => {
   expect(m.obsidian.vault.process).toBeTypeOf("function");
 
-  expect(m.utility.toSlug).toBeTypeOf("function");
   expect(m.utility.getFileName).toBeTypeOf("function");
   expect(m.utility.getFrontmatterAndMd).toBeTypeOf("function");
+  expect(m.utility.jsonStringify).toBeTypeOf("function");
+  expect(m.utility.toSlug).toBeTypeOf("function");
+  expect(m.utility.writeToFileSync).toBeTypeOf("function");
 });