diff -u b/core/lib/Drupal/Component/Scaffold/Handler.php b/core/lib/Drupal/Component/Scaffold/Handler.php
--- b/core/lib/Drupal/Component/Scaffold/Handler.php
+++ b/core/lib/Drupal/Component/Scaffold/Handler.php
@@ -9,9 +9,9 @@
 use Composer\Package\PackageInterface;
 use Composer\Plugin\CommandEvent;
 use Composer\Util\Filesystem;
-use Drupal\Component\Scaffold\Operations\OperationCollection;
 use Drupal\Component\Scaffold\Operations\OperationData;
 use Drupal\Component\Scaffold\Operations\OperationFactory;
+use Drupal\Component\Scaffold\Operations\ScaffoldFileCollection;
 
 /**
  * Core class of the plugin.
@@ -155,11 +155,15 @@
     $file_mappings = $this->getFileMappingsFromPackages($allowed_packages);
 
     // Analyze the list of file mappings, and determine which take priority.
-    $scaffold_collection = new OperationCollection($this->io);
     $location_replacements = $this->manageOptions->getLocationReplacements();
-
-    // Write the collected scaffold files to the designated location on disk.
-    $scaffold_results = $scaffold_collection->process($file_mappings, $location_replacements, $this->manageOptions->getOptions());
+    $scaffold_files = ScaffoldFileCollection::create($file_mappings, $location_replacements);
+    $scaffold_results = [];
+    // Process all of the files that were collated one package at a time.
+    iterator_apply(
+      $scaffold_files,
+      [ScaffoldFileCollection::class, 'process'],
+      [$scaffold_files, $this->io, $this->manageOptions->getOptions(), &$scaffold_results]
+    );
 
     // Generate an autoload file in the document root that includes the
     // autoload.php file in the vendor directory, wherever that is. Drupal
reverted:
--- b/core/lib/Drupal/Component/Scaffold/Operations/OperationCollection.php
+++ /dev/null
@@ -1,79 +0,0 @@
-<?php
-
-namespace Drupal\Component\Scaffold\Operations;
-
-use Composer\IO\IOInterface;
-use Drupal\Component\Scaffold\Interpolator;
-use Drupal\Component\Scaffold\ScaffoldOptions;
-
-/**
- * Manages and processes the collection of files to be scaffolded.
- */
-class OperationCollection {
-
-  /**
-   * Composer's I/O service.
-   *
-   * @var \Composer\IO\IOInterface
-   */
-  protected $io;
-
-  /**
-   * OperationCollection constructor.
-   *
-   * @param \Composer\IO\IOInterface $io
-   *   A reference to the IO object, to allow us to write progress messages
-   *   as we process scaffold operations.
-   */
-  public function __construct(IOInterface $io) {
-    $this->io = $io;
-  }
-
-  /**
-   * Process all of the scaffold files listed in the provided file mappings.
-   *
-   * @param array $file_mappings
-   *   An multidimensional array of file mappings, as returned by
-   *   self::getFileMappingsFromPackages().
-   * @param \Drupal\Component\Scaffold\Interpolator $location_replacements
-   *   An object with the location mappings (e.g. [web-root]).
-   * @param \Drupal\Component\Scaffold\ScaffoldOptions $options
-   *   Configuration options from the top-level composer.json file.
-   *
-   * @return \Drupal\Component\Scaffold\Operations\ScaffoldResult[]
-   *   Associative array keyed by destination path and values as the scaffold
-   *   result for each scaffolded file.
-   */
-  public function process(array $file_mappings, Interpolator $location_replacements, ScaffoldOptions $options) {
-    $collatedScaffoldFiles = new ScaffoldFileCollator($this->io);
-    $collatedScaffoldFiles->collateScaffoldFiles($file_mappings, $location_replacements);
-    return $this->processScaffoldFiles($collatedScaffoldFiles, $options);
-  }
-
-  /**
-   * Scaffolds the files in our scaffold collection, package-by-package.
-   *
-   * @param ScaffoldFileCollator $collatedScaffoldFiles
-   *   Collection of collated scaffold files.
-   * @param \Drupal\Component\Scaffold\ScaffoldOptions $options
-   *   Configuration options from the top-level composer.json file.
-   *
-   * @return \Drupal\Component\Scaffold\Operations\ScaffoldResult[]
-   *   Associative array keyed by destination path and values as the scaffold
-   *   result for each scaffolded file.
-   */
-  protected function processScaffoldFiles(ScaffoldFileCollator $collatedScaffoldFiles, ScaffoldOptions $options) {
-    $result = [];
-    // Process all of the files that were collated one package at a time.
-    foreach ($collatedScaffoldFiles->resolvedScaffoldFiles() as $package_name => $package_scaffold_files) {
-      $this->io->write("Scaffolding files for <comment>{$package_name}</comment>:");
-      foreach ($package_scaffold_files as $dest_rel_path => $scaffold_file) {
-        if (!$collatedScaffoldFiles->overridden($scaffold_file)) {
-          $result[$dest_rel_path] = $scaffold_file->process($this->io, $options);
-        }
-      }
-    }
-    return $result;
-  }
-
-}
reverted:
--- b/core/lib/Drupal/Component/Scaffold/Operations/ScaffoldFileCollator.php
+++ /dev/null
@@ -1,139 +0,0 @@
-<?php
-
-namespace Drupal\Component\Scaffold\Operations;
-
-use Composer\IO\IOInterface;
-use Drupal\Component\Scaffold\Interpolator;
-use Drupal\Component\Scaffold\ScaffoldFileInfo;
-use Drupal\Component\Scaffold\ScaffoldFilePath;
-
-/**
- * Collates the scaffold file for the OperationCollection class.
- */
-class ScaffoldFileCollator {
-
-  /**
-   * Composer's I/O service.
-   *
-   * @var \Composer\IO\IOInterface
-   */
-  protected $io;
-
-  /**
-   * Collation of all scaffold files.
-   *
-   * The top level array maps from the package name to the collection of
-   * scaffold files provided by that package. Each collection of scaffold files
-   * is keyed by destination path.
-   *
-   * @var \Drupal\Component\Scaffold\ScaffoldFileInfo[][]
-   */
-  protected $resolvedFileMappings = [];
-
-  /**
-   * Collection of all destination paths to be scaffolded.
-   *
-   * Each key maps to the last file to scaffold at each location.
-   *
-   * @var \Drupal\Component\Scaffold\ScaffoldFileInfo[]
-   */
-  protected $listOfScaffoldFiles = [];
-
-  /**
-   * OperationCollection constructor.
-   *
-   * @param \Composer\IO\IOInterface $io
-   *   A reference to the IO object, to allow us to write progress messages
-   *   as we process scaffold operations.
-   */
-  public function __construct(IOInterface $io) {
-    $this->io = $io;
-  }
-
-  /**
-   * Organizes provided file mappings by destination and package.
-   *
-   * @param array $file_mappings
-   *   An multidimensional array of file mappings, as returned by
-   *   self::getFileMappingsFromPackages().
-   * @param \Drupal\Component\Scaffold\Interpolator $location_replacements
-   *   An object with the location mappings (e.g. [web-root]).
-   */
-  public function collateScaffoldFiles(array $file_mappings, Interpolator $location_replacements) {
-    foreach ($file_mappings as $package_name => $package_file_mappings) {
-      foreach ($package_file_mappings as $destination_rel_path => $op) {
-        $destination = ScaffoldFilePath::destinationPath($package_name, $destination_rel_path, $location_replacements);
-        // If there was already a scaffolding operation happening at this path,
-        // and the new operation is Conjoinable, then use a ConjunctionOp to
-        // join together both operations. This will cause both operations to
-        // run, one after the other. At the moment, only AppendOp is
-        // conjoinable; all other operations simply replace anything at the same
-        // path.
-        if (isset($this->listOfScaffoldFiles[$destination_rel_path]) && $op instanceof ConjoinableInterface) {
-          $op = new ConjunctionOp($this->listOfScaffoldFiles[$destination_rel_path]->op(), $op);
-        }
-
-        $scaffold_file = new ScaffoldFileInfo($destination, $op);
-        $this->listOfScaffoldFiles[$destination_rel_path] = $scaffold_file;
-        $this->resolvedFileMappings[$package_name][$destination_rel_path] = $scaffold_file;
-      }
-    }
-  }
-
-  /**
-   * Provides access to the resolved scaffold files.
-   *
-   * @return \Drupal\Component\Scaffold\ScaffoldFileInfo[][]
-   *   Collation of all scaffold files.
-   */
-  public function resolvedScaffoldFiles() {
-    return $this->resolvedFileMappings;
-  }
-
-  /**
-   * Determines whether a given location has been overridden.
-   *
-   * As a side effect, reports a status message noting that the file was
-   * skipped.
-   *
-   * @param \Drupal\Component\Scaffold\ScaffoldFileInfo $scaffold_file
-   *   Scaffold file location to test overridden status.
-   *
-   * @return bool
-   *   TRUE if specified location is overridden by another package.
-   */
-  public function overridden(ScaffoldFileInfo $scaffold_file) {
-    $overriding_package = $this->findProvidingPackage($scaffold_file);
-    $overridden = $scaffold_file->overridden($overriding_package);
-    if ($overridden) {
-      $this->io->write($scaffold_file->interpolate("  - Skip <info>[dest-rel-path]</info>: overridden in <comment>{$overriding_package}</comment>"));
-    }
-    return $overridden;
-  }
-
-  /**
-   * Finds the package name that provides the scaffold file.
-   *
-   * This will usually be $scaffold_file->packageName(), unless there are
-   * multiple scaffold files with the same destination path. In the case
-   * that there are multiple scaffold files, the name of the last package
-   * that provided a scaffold file at that path will be returned.
-   *
-   * @param \Drupal\Component\Scaffold\ScaffoldFileInfo $scaffold_file
-   *   The scaffold file to use to find a providing package name.
-   *
-   * @return string
-   *   The name of the package that provided the scaffold file information.
-   */
-  protected function findProvidingPackage(ScaffoldFileInfo $scaffold_file) {
-    // The scaffold file should always be in our list, but we will check
-    // just to be sure that it really is.
-    $dest_rel_path = $scaffold_file->destination()->relativePath();
-    if (!array_key_exists($dest_rel_path, $this->listOfScaffoldFiles)) {
-      $msg = $scaffold_file->interpolate("  - Scaffold file [dest-rel-path] not found in list of all scaffold files.");
-      throw new \RuntimeException($msg);
-    }
-    return $this->listOfScaffoldFiles[$dest_rel_path]->packageName();
-  }
-
-}
diff -u b/core/lib/Drupal/Component/Scaffold/Operations/SkipOp.php b/core/lib/Drupal/Component/Scaffold/Operations/SkipOp.php
--- b/core/lib/Drupal/Component/Scaffold/Operations/SkipOp.php
+++ b/core/lib/Drupal/Component/Scaffold/Operations/SkipOp.php
@@ -17,11 +17,28 @@
   const ID = 'skip';
 
   /**
+   * The message to output while processing.
+   *
+   * @var string
+   */
+  protected $message;
+
+  /**
+   * SkipOp constructor.
+   *
+   * @param string $message
+   *   (optional) A custom message to output while skipping.
+   */
+  public function __construct($message = "  - Skip <info>[dest-rel-path]</info>: disabled") {
+    $this->message = $message;
+  }
+
+  /**
    * {@inheritdoc}
    */
   public function process(ScaffoldFilePath $destination, IOInterface $io, ScaffoldOptions $options) {
     $interpolator = $destination->getInterpolator();
-    $io->write($interpolator->interpolate("  - Skip <info>[dest-rel-path]</info>: disabled"));
+    $io->write($interpolator->interpolate($this->message));
     return new ScaffoldResult($destination, FALSE);
   }
 
reverted:
--- b/core/tests/Drupal/Tests/Component/Scaffold/Integration/ScaffoldFileCollatorTest.php
+++ /dev/null
@@ -1,131 +0,0 @@
-<?php
-
-namespace Drupal\Tests\Component\Scaffold\Integration;
-
-use PHPUnit\Framework\TestCase;
-use Drupal\Component\Scaffold\ScaffoldFileInfo;
-use Drupal\Tests\Component\Scaffold\Fixtures;
-use Drupal\Component\Scaffold\Operations\AppendOp;
-use Drupal\Component\Scaffold\Operations\ConjunctionOp;
-use Drupal\Component\Scaffold\Operations\SkipOp;
-use Drupal\Component\Scaffold\Operations\ScaffoldFileCollator;
-
-/**
- * @coversDefaultClass \Drupal\Component\Scaffold\Operations\ScaffoldFileCollator
- *
- * @group Scaffold
- */
-class ScaffoldFileCollatorTest extends TestCase {
-
-  /**
-   * @covers ::collateScaffoldFiles
-   */
-  public function testCollateScaffoldFiles() {
-    $fixtures = new Fixtures();
-    $locationReplacements = $fixtures->getLocationReplacements();
-    $scaffold_file_fixtures = [
-      'fixtures/drupal-assets-fixture' => [
-        '[web-root]/index.php' => $fixtures->replaceOp('drupal-assets-fixture', 'index.php'),
-        '[web-root]/.htaccess' => $fixtures->replaceOp('drupal-assets-fixture', '.htaccess'),
-        '[web-root]/robots.txt' => $fixtures->replaceOp('drupal-assets-fixture', 'robots.txt'),
-        '[web-root]/sites/default/default.services.yml' => $fixtures->replaceOp('drupal-assets-fixture', 'default.services.yml'),
-      ],
-      'fixtures/drupal-profile' => [
-        '[web-root]/sites/default/default.services.yml' => $fixtures->replaceOp('drupal-profile', 'profile.default.services.yml'),
-      ],
-      'fixtures/drupal-drupal' => [
-        '[web-root]/.htaccess' => new SkipOp(),
-        '[web-root]/robots.txt' => $fixtures->appendOp('drupal-drupal-test-append', 'append-to-robots.txt'),
-      ],
-    ];
-    $sut = new ScaffoldFileCollator($fixtures->io());
-    // Test the system under test.
-    $sut->collateScaffoldFiles($scaffold_file_fixtures, $locationReplacements);
-    $scaffold_list = $this->accessProtected($sut, 'listOfScaffoldFiles');
-    $resolved_file_mappings = $sut->resolvedScaffoldFiles();
-    // Confirm that the keys of the output are the same as the keys of the
-    // input.
-    $this->assertEquals(array_keys($scaffold_file_fixtures), array_keys($resolved_file_mappings));
-    // Also assert that we have the right ScaffoldFileInfo objects in the
-    // destination.
-    $this->assertResolvedToSameOp('fixtures/drupal-assets-fixture', '[web-root]/index.php', $scaffold_file_fixtures, $scaffold_list, $resolved_file_mappings);
-    $this->assertResolvedToSameOp('fixtures/drupal-profile', '[web-root]/sites/default/default.services.yml', $scaffold_file_fixtures, $scaffold_list, $resolved_file_mappings);
-    $this->assertResolvedToSameOp('fixtures/drupal-drupal', '[web-root]/robots.txt', $scaffold_file_fixtures, $scaffold_list, $resolved_file_mappings);
-    // Assert that the files below have been overridden.
-    $this->assertOverridden('fixtures/drupal-assets-fixture', '[web-root]/.htaccess', $scaffold_list, $resolved_file_mappings);
-    $this->assertOverridden('fixtures/drupal-assets-fixture', '[web-root]/robots.txt', $scaffold_list, $resolved_file_mappings);
-  }
-
-  /**
-   * Checks to see if a given file was not overridden.
-   *
-   * The package name in the scaffold list for the provided destination should
-   * match the package name from the specified project.
-   *
-   * @param string $project
-   *   The project to check.
-   * @param string $dest
-   *   The destination to check.
-   * @param array $scaffold_file_fixtures
-   *   The test file mappings keyed by project and destination.
-   * @param \Drupal\Component\Scaffold\ScaffoldFileInfo[] $scaffold_list
-   *   The list of scaffolded files keyed by destination.
-   * @param array $resolved_file_mappings
-   *   The list of resolved file mappings keyed by project and destination.
-   */
-  protected function assertResolvedToSameOp($project, $dest, array $scaffold_file_fixtures, array $scaffold_list, array $resolved_file_mappings) {
-    $resolved_file_info = $resolved_file_mappings[$project][$dest];
-    $this->assertEquals(get_class($resolved_file_info), ScaffoldFileInfo::class);
-    $resolved_scaffold_op = $resolved_file_info->op();
-    // If this is an append op then it will be part of a conjunction op.
-    $expected = get_class($scaffold_file_fixtures[$project][$dest]);
-    if ($expected == AppendOp::class) {
-      $this->assertEquals(ConjunctionOp::class, get_class($resolved_scaffold_op));
-    }
-    else {
-      $this->assertEquals($expected, get_class($resolved_scaffold_op));
-      $this->assertEquals($scaffold_file_fixtures[$project][$dest], $resolved_scaffold_op);
-    }
-    $this->assertEquals($project, $scaffold_list[$dest]->packageName());
-  }
-
-  /**
-   * Checks if a given file was overridden.
-   *
-   * Assert that the file in the scaffold list at the specified destination
-   * comes from a different package than the one in the file info.
-   *
-   * @param string $project
-   *   The project to check.
-   * @param string $dest
-   *   The destination to check.
-   * @param \Drupal\Component\Scaffold\ScaffoldFileInfo[] $scaffold_list
-   *   The list of scaffolded files keyed by destination.
-   * @param array $resolved_file_mappings
-   *   The list of resolved file mappings keyed by project and destination.
-   */
-  protected function assertOverridden($project, $dest, array $scaffold_list, array $resolved_file_mappings) {
-    $resolved_file_info = $resolved_file_mappings[$project][$dest];
-    $this->assertEquals(get_class($resolved_file_info), ScaffoldFileInfo::class);
-    $this->assertNotEquals($project, $scaffold_list[$dest]->packageName());
-  }
-
-  /**
-   * Uses reflection to access a protected field of an object.
-   *
-   * @param mixed $obj
-   *   The object to inspect.
-   * @param string $prop
-   *   The name of the property to access.
-   *
-   * @return mixed
-   *   The value of the requested property.
-   */
-  protected function accessProtected($obj, $prop) {
-    $reflection = new \ReflectionClass($obj);
-    $property = $reflection->getProperty($prop);
-    $property->setAccessible(TRUE);
-    return $property->getValue($obj);
-  }
-
-}
only in patch2:
unchanged:
--- /dev/null
+++ b/core/lib/Drupal/Component/Scaffold/Operations/ScaffoldFileCollection.php
@@ -0,0 +1,103 @@
+<?php
+
+namespace Drupal\Component\Scaffold\Operations;
+
+use Composer\IO\IOInterface;
+use Drupal\Component\Scaffold\Interpolator;
+use Drupal\Component\Scaffold\ScaffoldFileInfo;
+use Drupal\Component\Scaffold\ScaffoldFilePath;
+use Drupal\Component\Scaffold\ScaffoldOptions;
+use RecursiveIterator;
+
+/**
+ * Collection of scaffold files.
+ */
+final class ScaffoldFileCollection {
+
+  /**
+   * ScaffoldFileCollection constructor.
+   */
+  private function __construct() {
+    // This class only provides static methods.
+  }
+
+  /**
+   * ScaffoldFileCollection constructor.
+   *
+   * @param array $file_mappings
+   *   An multidimensional array of file mappings, as returned by
+   *   self::getFileMappingsFromPackages().
+   * @param \Drupal\Component\Scaffold\Interpolator $location_replacements
+   *   An object with the location mappings (e.g. [web-root]).
+   *
+   * @return \RecursiveArrayIterator
+   *   An iterator on a multi-dimensional array of ScaffoldFileInfo objects
+   *   keyed by the project and the destination path.
+   *
+   * @see \Drupal\Component\Scaffold\ScaffoldFileInfo
+   */
+  public static function create(array $file_mappings, Interpolator $location_replacements) {
+    // Collection of all destination paths to be scaffolded. Used to determine
+    // when two project scaffold the same file and we have to skip or use a
+    // ConjunctionOp.
+    $scaffoldFiles = [];
+
+    // Collection of all destination paths to be scaffolded by project.
+    $scaffoldFilesByProject = [];
+
+    foreach ($file_mappings as $package_name => $package_file_mappings) {
+      foreach ($package_file_mappings as $destination_rel_path => $op) {
+        $destination = ScaffoldFilePath::destinationPath($package_name, $destination_rel_path, $location_replacements);
+        // If there was already a scaffolding operation happening at this path,
+        // and the new operation is Conjoinable, then use a ConjunctionOp to
+        // join together both operations. This will cause both operations to
+        // run, one after the other. At the moment, only AppendOp is
+        // conjoinable; all other operations simply replace anything at the same
+        // path.
+        if (isset($scaffoldFiles[$destination_rel_path])) {
+          $previous_scaffold_file = $scaffoldFiles[$destination_rel_path];
+          if ($op instanceof ConjoinableInterface) {
+            $op = new ConjunctionOp($previous_scaffold_file->op(), $op);
+            // Remove the previous file so we only do the operation once.
+            unset($scaffoldFilesByProject[$previous_scaffold_file->packageName()][$destination_rel_path]);
+          }
+          else {
+            $message = "  - Skip <info>[dest-rel-path]</info>: overridden in <comment>{$package_name}</comment>";
+            $scaffoldFilesByProject[$previous_scaffold_file->packageName()][$destination_rel_path] = new ScaffoldFileInfo($destination, new SkipOp($message));
+          }
+        }
+        $scaffold_file = new ScaffoldFileInfo($destination, $op);
+        $scaffoldFiles[$destination_rel_path] = $scaffold_file;
+        $scaffoldFilesByProject[$package_name][$destination_rel_path] = $scaffold_file;
+      }
+    }
+    return new \RecursiveArrayIterator($scaffoldFilesByProject, \RecursiveArrayIterator::CHILD_ARRAYS_ONLY);
+  }
+
+  /**
+   * Processes the iterator created by ScaffoldFileCollection::create().
+   *
+   * @param \RecursiveIterator $iterator
+   *   The iterator to process.
+   * @param \Composer\IO\IOInterface $io
+   *   The Composer IO object.
+   * @param \Drupal\Component\Scaffold\ScaffoldOptions $scaffold_options
+   *   The scaffold options.
+   * @param \Drupal\Component\Scaffold\Operations\ScaffoldResult[] $results
+   *   The results array, passed by-reference and is populated by this method.
+   */
+  public static function process(RecursiveIterator $iterator, IOInterface $io, ScaffoldOptions $scaffold_options, array &$results) {
+    while ($iterator->valid()) {
+      if ($iterator->hasChildren()) {
+        $io->write("Scaffolding files for <comment>{$iterator->key()}</comment>:");
+        static::process($iterator->getChildren(), $io, $scaffold_options, $results);
+      }
+      else {
+        $scaffold_file = $iterator->current();
+        $results[$scaffold_file->destination()->relativePath()] = $scaffold_file->process($io, $scaffold_options);
+      }
+      $iterator->next();
+    }
+  }
+
+}
only in patch2:
unchanged:
--- /dev/null
+++ b/core/tests/Drupal/Tests/Component/Scaffold/Integration/ScaffoldFileCollectionTest.php
@@ -0,0 +1,67 @@
+<?php
+
+namespace Drupal\Tests\Component\Scaffold\Integration;
+
+use PHPUnit\Framework\TestCase;
+use Drupal\Tests\Component\Scaffold\Fixtures;
+use Drupal\Component\Scaffold\Operations\ConjunctionOp;
+use Drupal\Component\Scaffold\Operations\SkipOp;
+use Drupal\Component\Scaffold\Operations\ScaffoldFileCollection;
+
+/**
+ * @coversDefaultClass \Drupal\Component\Scaffold\Operations\ScaffoldFileCollection
+ *
+ * @group Scaffold
+ */
+class ScaffoldFileCollectionTest extends TestCase {
+
+  /**
+   * @covers ::create
+   */
+  public function testCreate() {
+    $fixtures = new Fixtures();
+    $locationReplacements = $fixtures->getLocationReplacements();
+    $scaffold_file_fixtures = [
+      'fixtures/drupal-assets-fixture' => [
+        '[web-root]/index.php' => $fixtures->replaceOp('drupal-assets-fixture', 'index.php'),
+        '[web-root]/.htaccess' => $fixtures->replaceOp('drupal-assets-fixture', '.htaccess'),
+        '[web-root]/robots.txt' => $fixtures->replaceOp('drupal-assets-fixture', 'robots.txt'),
+        '[web-root]/sites/default/default.services.yml' => $fixtures->replaceOp('drupal-assets-fixture', 'default.services.yml'),
+      ],
+      'fixtures/drupal-profile' => [
+        '[web-root]/sites/default/default.services.yml' => $fixtures->replaceOp('drupal-profile', 'profile.default.services.yml'),
+      ],
+      'fixtures/drupal-drupal' => [
+        '[web-root]/.htaccess' => new SkipOp(),
+        '[web-root]/robots.txt' => $fixtures->appendOp('drupal-drupal-test-append', 'append-to-robots.txt'),
+      ],
+    ];
+    $sut = ScaffoldFileCollection::create($scaffold_file_fixtures, $locationReplacements);
+    $resolved_file_mappings = iterator_to_array($sut);
+    // Confirm that the keys of the output are the same as the keys of the
+    // input.
+    $this->assertEquals(array_keys($scaffold_file_fixtures), array_keys($resolved_file_mappings));
+    // Ensure that '[web-root]/robots.txt' has been removed as it is now part of
+    // a conjunction operation.
+    $this->assertEquals([
+      '[web-root]/index.php',
+      '[web-root]/.htaccess',
+      '[web-root]/sites/default/default.services.yml',
+    ], array_keys($resolved_file_mappings['fixtures/drupal-assets-fixture']));
+
+    $this->assertEquals([
+      '[web-root]/sites/default/default.services.yml',
+    ], array_keys($resolved_file_mappings['fixtures/drupal-profile']));
+
+    $this->assertEquals([
+      '[web-root]/.htaccess',
+      '[web-root]/robots.txt',
+    ], array_keys($resolved_file_mappings['fixtures/drupal-drupal']));
+
+    // Test that .htaccess is skipped.
+    $this->assertInstanceOf(SkipOp::class, $resolved_file_mappings['fixtures/drupal-assets-fixture']['[web-root]/.htaccess']->op());
+    // Test that the expected conjunction operation exists.
+    $this->assertInstanceOf(ConjunctionOp::class, $resolved_file_mappings['fixtures/drupal-drupal']['[web-root]/robots.txt']->op());
+  }
+
+}