Add testcase for #381

Relates to and shows that #381 is not an issue anymore.

Closes #381

tests/AppendPagesTest.js

@@ -1,5 +1,7 @@
 const muhammara = require("../lib/muhammara");
+const Recipe = require("../lib/Recipe");
 const expect = require("chai").expect;
+const fs = require("fs");
 
 describe("AppendPagesTest", function () {
   it("should complete without error", function () {
@@ -26,4 +28,19 @@ describe("AppendPagesTest", function () {
       ),
     ).to.throw("unable to append");
   });
+
+  it("should free the file handle", () => {
+    const testFile1 = __dirname + "/output/test1.pdf";
+    const testFile2 = __dirname + "/output/test2.pdf";
+    const resultFile = __dirname + "/output/result.pdf";
+    fs.copyFileSync(__dirname + "/TestMaterials/Original.pdf", testFile1);
+    fs.copyFileSync(__dirname + "/TestMaterials/Original.pdf", testFile2);
+
+    const pdfDoc = new Recipe(testFile1, resultFile);
+    pdfDoc.appendPage(testFile2).endPDF();
+
+    // error here: Error: EBUSY: resource busy or locked, unlink
+    fs.unlinkSync(testFile1);
+    fs.unlinkSync(testFile2);
+  });
 });