diff --git a/test/lib/next-modes/base.ts b/test/lib/next-modes/base.ts
index 955e0f3bbe55b..1eba7c5f1f2d3 100644
--- a/test/lib/next-modes/base.ts
+++ b/test/lib/next-modes/base.ts
@@ -154,6 +154,18 @@ export class NextInstance {
     }
 
     const tempNodeModulesFolder = 'node_modules_bak'
+    // Merge customized node_modules and installed node_modules.
+    // Move files[node_modules] to a temporary folder node_modules_back,
+    // then copy the modules back to node_modules after installation.
+    const tempNodeModulesPath = path.join(this.testDir, tempNodeModulesFolder)
+    const nodeModulesDir = path.join(this.testDir, 'node_modules')
+    const nodeModulesStats = await fs.stat(nodeModulesDir)
+    const hasNodeModulesDir = nodeModulesStats.isDirectory()
+    if (hasNodeModulesDir) {
+      // Move node_modules to temp folder
+      await fs.move(nodeModulesDir, tempNodeModulesPath)
+    }
+
     if (this.files instanceof FileRef) {
       // if a FileRef is passed directly to `files` we copy the
       // entire folder to the test directory
@@ -165,35 +177,11 @@ export class NextInstance {
         )
       }
 
-      // Merge customized node_modules and installed node_modules.
-      // Move files[node_modules] to a temporary folder node_modules_back,
-      // then copy the modules back to node_modules after installation.
-      const tempNodeModulesPath = path.join(this.testDir, tempNodeModulesFolder)
-      const nodeModulesDir = path.join(this.testDir, 'node_modules')
-      const nodeModulesStats = await fs.stat(this.files.fsPath)
-      const hasNodeModulesDir = nodeModulesStats.isDirectory()
-      if (hasNodeModulesDir) {
-        // Move node_modules to temp folder
-        await fs.move(nodeModulesDir, tempNodeModulesPath)
-      }
       await fs.copy(this.files.fsPath, this.testDir)
-      if (hasNodeModulesDir) {
-        // Move node_modules from temp back to origin
-        await fs.copy(tempNodeModulesPath, nodeModulesDir)
-        await fs.remove(tempNodeModulesPath)
-      }
     } else {
-      let nodeModulesFolder: string | undefined
       for (const filename of Object.keys(this.files)) {
         const item = this.files[filename]
         let outputFilename = path.join(this.testDir, filename)
-        if (filename === 'node_modules') {
-          nodeModulesFolder = path.join(
-            this.testDir,
-            typeof item === 'string' ? item : item.fsPath
-          )
-          outputFilename = path.join(this.testDir, tempNodeModulesFolder)
-        }
 
         if (typeof item === 'string') {
           await fs.ensureDir(path.dirname(outputFilename))
@@ -202,14 +190,12 @@ export class NextInstance {
           await fs.copy(item.fsPath, outputFilename)
         }
       }
+    }
 
-      if (nodeModulesFolder) {
-        await fs.copy(
-          nodeModulesFolder,
-          path.join(this.testDir, 'node_modules')
-        )
-        await fs.remove(nodeModulesFolder)
-      }
+    if (hasNodeModulesDir) {
+      // Move node_modules from temp back to origin
+      await fs.copy(tempNodeModulesPath, nodeModulesDir)
+      await fs.remove(tempNodeModulesPath)
     }
 
     let nextConfigFile = Object.keys(this.files).find((file) =>