fixed nested test with explanatory comment

Author: samdeane

Tests/SwiftFormatTests/Core/IgnoreFileTests.swift

@@ -118,9 +118,17 @@ final class IgnoreFileTests: XCTestCase {
     XCTAssertNotNil(try IgnoreFile(for: url.appending(path: "Source/Ignored/file.swift")))
     let iterator = FileIterator(urls: [url], followSymlinks: false)
     let files = Array(iterator)
-    print(files)
-    XCTAssertEqual(files.count, 1)
-    XCTAssertEqual(files.first?.lastPathComponent, "file.swift")
+
+    // note that the ignore file has no effect on the FileIterator here,
+    // because it is not in the root directory
+    // this is expected behavior, and a limitation of the current implementation
+    // of FileIterator, as it flattens subdirectories into a single list rather
+    // than recursing into them; however, the ignore file itself will still be
+    // picked up and obeyed when each source file is processed.
+    XCTAssertEqual(files.count, 2)
+    for file in files {
+      XCTAssertEqual(file.lastPathComponent, "file.swift")
+    }
   }
 
 }