diff --git a/Sources/AppKit/CocoaCollectionViewDiffableDataSource.swift b/Sources/AppKit/CocoaCollectionViewDiffableDataSource.swift
index aa5eb7e..2d837d5 100644
--- a/Sources/AppKit/CocoaCollectionViewDiffableDataSource.swift
+++ b/Sources/AppKit/CocoaCollectionViewDiffableDataSource.swift
@@ -35,7 +35,7 @@ open class CocoaCollectionViewDiffableDataSource<SectionIdentifierType: Hashable
     ///                           diffing animation.
     ///   - completion: An optional completion block which is called when the complete
     ///                 performing updates.
-    public func apply(_ snapshot: DiffableDataSourceSnapshot<SectionIdentifierType, ItemIdentifierType>, animatingDifferences: Bool = true) {
+    public func apply(_ snapshot: DiffableDataSourceSnapshot<SectionIdentifierType, ItemIdentifierType>, animatingDifferences: Bool = true, completion: (() -> Void)? = nil) {
         core.apply(
             snapshot,
             view: collectionView,
diff --git a/Tests/CocoaCollectionViewDiffableDataSourceTests.swift b/Tests/CocoaCollectionViewDiffableDataSourceTests.swift
index ca54824..c500e01 100644
--- a/Tests/CocoaCollectionViewDiffableDataSourceTests.swift
+++ b/Tests/CocoaCollectionViewDiffableDataSourceTests.swift
@@ -22,21 +22,29 @@ final class CocoaCollectionViewDiffableDataSourceTests: XCTestCase {
 
         var snapshot = DiffableDataSourceSnapshot<Int, Int>()
 
-        dataSource.apply(snapshot)
+        let e1 = expectation(description: "testApply() e1")
+        dataSource.apply(snapshot, completion: e1.fulfill)
+        wait(for: [e1], timeout: 1)
         XCTAssertEqual(collectionView.isPerformBatchUpdatesCalledCount, 0)
 
         snapshot.appendSections([0])
         snapshot.appendItems([0])
 
-        dataSource.apply(snapshot)
+        let e2 = expectation(description: "testApply() e2")
+        dataSource.apply(snapshot, completion: e2.fulfill)
+        wait(for: [e2], timeout: 1)
         XCTAssertEqual(collectionView.isPerformBatchUpdatesCalledCount, 1)
 
-        dataSource.apply(snapshot)
+        let e3 = expectation(description: "testApply() e3")
+        dataSource.apply(snapshot, completion: e3.fulfill)
+        wait(for: [e3], timeout: 1)
         XCTAssertEqual(collectionView.isPerformBatchUpdatesCalledCount, 1)
 
         snapshot.appendItems([1])
 
-        dataSource.apply(snapshot)
+        let e4 = expectation(description: "testApply() e4")
+        dataSource.apply(snapshot, completion: e4.fulfill)
+        wait(for: [e4], timeout: 1)
         XCTAssertEqual(collectionView.isPerformBatchUpdatesCalledCount, 2)
     }
 
diff --git a/Tests/CollectionViewDiffableDataSourceTests.swift b/Tests/CollectionViewDiffableDataSourceTests.swift
index e419a54..872683a 100644
--- a/Tests/CollectionViewDiffableDataSourceTests.swift
+++ b/Tests/CollectionViewDiffableDataSourceTests.swift
@@ -22,21 +22,29 @@ final class CollectionViewDiffableDataSourceTests: XCTestCase {
 
         var snapshot = DiffableDataSourceSnapshot<Int, Int>()
 
-        dataSource.apply(snapshot)
+        let e1 = expectation(description: "testApply() e1")
+        dataSource.apply(snapshot, completion: e1.fulfill)
+        wait(for: [e1], timeout: 1)
         XCTAssertEqual(collectionView.isPerformBatchUpdatesCalledCount, 0)
 
         snapshot.appendSections([0])
         snapshot.appendItems([0])
 
-        dataSource.apply(snapshot)
+        let e2 = expectation(description: "testApply() e2")
+        dataSource.apply(snapshot, completion: e2.fulfill)
+        wait(for: [e2], timeout: 1)
         XCTAssertEqual(collectionView.isPerformBatchUpdatesCalledCount, 1)
 
-        dataSource.apply(snapshot)
+        let e3 = expectation(description: "testApply() e3")
+        dataSource.apply(snapshot, completion: e3.fulfill)
+        wait(for: [e3], timeout: 1)
         XCTAssertEqual(collectionView.isPerformBatchUpdatesCalledCount, 1)
 
         snapshot.appendItems([1])
 
-        dataSource.apply(snapshot)
+        let e4 = expectation(description: "testApply() e4")
+        dataSource.apply(snapshot, completion: e4.fulfill)
+        wait(for: [e4], timeout: 1)
         XCTAssertEqual(collectionView.isPerformBatchUpdatesCalledCount, 2)
     }
 
diff --git a/Tests/TableViewDiffableDataSourceTests.swift b/Tests/TableViewDiffableDataSourceTests.swift
index c29cd3f..ce3e1cb 100644
--- a/Tests/TableViewDiffableDataSourceTests.swift
+++ b/Tests/TableViewDiffableDataSourceTests.swift
@@ -22,21 +22,29 @@ final class TableViewDiffableDataSourceTests: XCTestCase {
 
         var snapshot = DiffableDataSourceSnapshot<Int, Int>()
 
-        dataSource.apply(snapshot)
+        let e1 = expectation(description: "testApply() e1")
+        dataSource.apply(snapshot, completion: e1.fulfill)
+        wait(for: [e1], timeout: 1)
         XCTAssertEqual(tableView.isPerformBatchUpdatesCalledCount, 0)
 
         snapshot.appendSections([0])
         snapshot.appendItems([0])
 
-        dataSource.apply(snapshot)
+        let e2 = expectation(description: "testApply() e2")
+        dataSource.apply(snapshot, completion: e2.fulfill)
+        wait(for: [e2], timeout: 1)
         XCTAssertEqual(tableView.isPerformBatchUpdatesCalledCount, 1)
 
-        dataSource.apply(snapshot)
+        let e3 = expectation(description: "testApply() e3")
+        dataSource.apply(snapshot, completion: e3.fulfill)
+        wait(for: [e3], timeout: 1)
         XCTAssertEqual(tableView.isPerformBatchUpdatesCalledCount, 1)
 
         snapshot.appendItems([1])
 
-        dataSource.apply(snapshot)
+        let e4 = expectation(description: "testApply() e4")
+        dataSource.apply(snapshot, completion: e4.fulfill)
+        wait(for: [e4], timeout: 1)
         XCTAssertEqual(tableView.isPerformBatchUpdatesCalledCount, 2)
     }