fix solution

src/app.js

@@ -1,37 +1,7 @@
 'use strict';
 
-const fs = require('fs');
-const path = require('path');
+const { customCopyFile } = require('./modules/customCopyFile');
 
-const customCopyFile = () => {
-  const inputArgs = process.argv.slice(2);
+const [sourceFile, destinationFile] = process.argv.slice(2);
 
-  if (inputArgs.length !== 2) {
-    process.stderr.write('should be 2 params');
-
-    return;
-  }
-
-  const [sourceFile, destinationFile] = inputArgs;
-
-  if (sourceFile === destinationFile) {
-    return;
-  }
-
-  const sourcePath = path.join(__dirname, '..', sourceFile);
-  const destinationPath = path.join(__dirname, '..', destinationFile);
-
-  try {
-    fs.copyFileSync(sourcePath, destinationPath);
-  } catch (err) {
-    if (err.code === 'EISDIR' || err.code === 'EPERM') {
-      process.stderr.write('source or destination is a directory');
-    }
-
-    if (err.code === 'ENOENT') {
-      process.stderr.write('non-existent source file');
-    }
-  }
-};
-
-customCopyFile();
+customCopyFile(sourceFile, destinationFile);

src/modules/customCopyFile.js

@@ -0,0 +1,35 @@
+'use strict';
+
+const fs = require('fs');
+const path = require('path');
+
+const customCopyFile = (sourceFile, destinationFile) => {
+  if (sourceFile === undefined || destinationFile === undefined) {
+    process.stderr.write('should be 2 params');
+
+    return;
+  }
+
+  if (sourceFile === destinationFile) {
+    return;
+  }
+
+  const sourcePath = path.join(__dirname, '..', '..', sourceFile);
+  const destinationPath = path.join(__dirname, '..', '..', destinationFile);
+
+  try {
+    fs.copyFileSync(sourcePath, destinationPath);
+  } catch (err) {
+    if (err.code === 'EISDIR' || err.code === 'EPERM') {
+      process.stderr.write('source or destination is a directory');
+    }
+
+    if (err.code === 'ENOENT') {
+      process.stderr.write('non-existent source file');
+    }
+  }
+};
+
+module.exports = {
+  customCopyFile,
+};