Add a couple more tests (#4)

test/test.js

@@ -6,6 +6,18 @@ const assert = require('assert').strict;
 const detective = require('../index.js');
 
 describe('detective-vue2', () => {
+  it('throws if the source content is not given', () => {
+    assert.throws(() => {
+      detective();
+    }, /^Error: content not given$/);
+  });
+
+  it('throws if the source content is not given', () => {
+    assert.throws(() => {
+      detective(() => {});
+    }, /^Error: content is not a string$/);
+  });
+
   it('retrieves the dependencies of script block lang ts', () => {
     const deps = detective('<template></template> <script lang="ts">import {foo, bar} from "mylib"; </script>');
     assert.equal(deps.length, 1);