fix one test and add comments

Author: silverwind

tests/src/rules/no-unused-modules.js

@@ -1304,6 +1304,7 @@ describe('support ES2022 Arbitrary module namespace identifier names', () => {
 });
 
 describe('parser ignores prefixes like BOM and hashbang', () => {
+  // bom, hashbang
   ruleTester.run('no-unused-modules', rule, {
     valid: [
       test({
@@ -1313,12 +1314,13 @@ describe('parser ignores prefixes like BOM and hashbang', () => {
       }),
       test({
         options: unusedExportsOptions,
-        code: `\uFEFFimport {foo} from './prefix-child.js';\n`,
+        code: `\uFEFF#!/usr/bin/env node\nimport {foo} from './prefix-child.js';\n`,
         filename: testFilePath('./no-unused-modules/prefix-parent-bom.js'),
       }),
     ],
     invalid: [],
   });
+  // no bom, hashbang
   ruleTester.run('no-unused-modules', rule, {
     valid: [
       test({
@@ -1334,6 +1336,7 @@ describe('parser ignores prefixes like BOM and hashbang', () => {
     ],
     invalid: [],
   });
+  // bom, no hashbang
   ruleTester.run('no-unused-modules', rule, {
     valid: [
       test({
@@ -1349,6 +1352,7 @@ describe('parser ignores prefixes like BOM and hashbang', () => {
     ],
     invalid: [],
   });
+  // no bom, no hashbang
   ruleTester.run('no-unused-modules', rule, {
     valid: [
       test({