Fix looking up multipart form temporary files (#781)

Tests/WordPressKitTests/Tests/Utilities/URLSessionHelperTests.swift

@@ -269,7 +269,7 @@ class URLSessionHelperTests: XCTestCase {
  }
 
  // Capture a list of files in temp dirs, before calling the upload function.
- let tempFilesBeforeUpload = existingTempFiles()
+ let tempFilesBeforeUpload = try existingMultipartFormTempFiles()
 
  // Perform upload HTTP request
  let builder = try HTTPRequestBuilder(url: URL(string: "https://wordpress.org/upload")!)
@@ -278,7 +278,7 @@ class URLSessionHelperTests: XCTestCase {
  let _ = await session.perform(request: builder, errorType: TestError.self)
 
  // Capture a list of files in the temp dirs, after calling the upload function.
- let tempFilesAfterUpload = existingTempFiles()
+ let tempFilesAfterUpload = try existingMultipartFormTempFiles()
 
  // There should be no new files after the HTTP request returns. This assertion relies on an implementation detail
  // where the multipart form content is put into a file in temp dirs.
@@ -299,7 +299,7 @@ class URLSessionHelperTests: XCTestCase {
  }
 
  // Capture a list of files in temp dirs, before calling the upload function.
- let tempFilesBeforeUpload = existingTempFiles()
+ let tempFilesBeforeUpload = try existingMultipartFormTempFiles()
 
  // Perform upload HTTP request
  let builder = try HTTPRequestBuilder(url: URL(string: "https://wordpress.org/upload")!)
@@ -308,28 +308,21 @@ class URLSessionHelperTests: XCTestCase {
  let _ = await session.perform(request: builder, errorType: TestError.self)
 
  // Capture a list of files in the temp dirs, after calling the upload function.
- let tempFilesAfterUpload = existingTempFiles()
+ let tempFilesAfterUpload = try existingMultipartFormTempFiles()
 
  // There should be no new files after the HTTP request returns. This assertion relies on an implementation detail
  // where the multipart form content is put into a file in temp dirs.
  let newFiles = tempFilesAfterUpload.subtracting(tempFilesBeforeUpload)
  XCTAssertEqual(newFiles.count, 0)
  }
 
- private func existingTempFiles() -> Set<String> {
+ // This functions finds temp files that are used for uploading multipart form.
+ // The implementation relies on an internal implementation detail of building multipart form content.
+ private func existingMultipartFormTempFiles() throws -> Set<String> {
  let fm = FileManager.default
- let enumerators = [
- fm.enumerator(atPath: NSTemporaryDirectory()),
- fm.enumerator(atPath: fm.temporaryDirectory.path)
- ].compactMap { $0 }
-
- var result: Set<String> = []
- for enumerator in enumerators {
- while let file = enumerator.nextObject() as? String {
- result.insert(file)
- }
- }
- return result
+ let files = try fm.contentsOfDirectory(atPath: fm.temporaryDirectory.path)
+ .filter { UUID(uuidString: $0) != nil }
+ return Set(files)
  }
 
  private func createLargeFile(megaBytes: Int) throws -> URL {