message: Create a custom matcher
diff: @@ -128,13 +128,21 @@ someVariable = 'newValue';`
  it("should not match a 'const' declaration", async () => {
  const editor = new InMemoryEditor(`const aVariable[cursor] = "value";`);
  - const is_matching = await isMatchingVisitor(editor.code, (onMatch) =>
  + await expectVisitorWontMatch(editor);
  + });
  +});
  +
  +async function expectVisitorWontMatch(editor: InMemoryEditor) {
  + const isMatching = await isMatchingVisitor(editor.code, (onMatch) =>
  createVisitor(editor.selection, () => onMatch())
  );
  - expect(is_matching).toBe(false);
  - });
  -});
  + try {
  + expect(isMatching).toBe(false);
  + } catch (error) {
  + throw new Error("Visitor matches given code but shouldn't");
  + }
  +}
  function isMatchingVisitor(
  code: Code,
  