diff --git a/spec/lib/file_store/s3_store_spec.rb b/spec/lib/file_store/s3_store_spec.rb
index 639927a95d..346ad44000 100644
--- a/spec/lib/file_store/s3_store_spec.rb
+++ b/spec/lib/file_store/s3_store_spec.rb
@@ -10,6 +10,7 @@ describe FileStore::S3Store do
   let(:resource) { Aws::S3::Resource.new(client: client) }
   let(:s3_bucket) { resource.bucket("s3-upload-bucket") }
   let(:s3_object) { stub }
+  let(:upload_path) { Discourse.store.upload_path }
 
   fab!(:optimized_image) { Fabricate(:optimized_image) }
   let(:optimized_image_file) { file_from_fixtures("logo.png") }
@@ -191,22 +192,21 @@ describe FileStore::S3Store do
   context 'copying files in S3' do
     describe '#copy_file' do
       it "copies the from in S3 with the right paths" do
-        s3_helper.expects(:s3_bucket).returns(s3_bucket)
-
         upload.update!(
           url: "//s3-upload-bucket.s3.dualstack.us-west-1.amazonaws.com/original/1X/#{upload.sha1}.png"
         )
 
-        source = Discourse.store.get_path_for_upload(upload)
-        destination = Discourse.store.get_path_for_upload(upload).sub('.png', '.jpg')
+        source = "#{upload_path}/#{Discourse.store.get_path_for_upload(upload)}"
+        destination = source.sub('.png', '.jpg')
+        bucket = prepare_fake_s3(source, upload)
 
-        s3_object = stub
-
-        s3_bucket.expects(:object).with(destination).returns(s3_object)
-
-        expect_copy_from(s3_object, "s3-upload-bucket/#{source}")
+        expect(bucket.find_object(source)).to be_present
+        expect(bucket.find_object(destination)).to be_nil
 
         store.copy_file(upload.url, source, destination)
+
+        expect(bucket.find_object(source)).to be_present
+        expect(bucket.find_object(destination)).to be_present
       end
     end
   end
@@ -214,33 +214,19 @@ describe FileStore::S3Store do
   context 'removal from s3' do
     describe "#remove_upload" do
       it "removes the file from s3 with the right paths" do
-        s3_helper.expects(:s3_bucket).returns(s3_bucket).at_least_once
-        upload.update!(url: "//s3-upload-bucket.s3.dualstack.us-west-1.amazonaws.com/original/1X/#{upload.sha1}.png")
-        s3_object = stub
+        upload_key = Discourse.store.get_path_for_upload(upload)
+        tombstone_key = "tombstone/#{upload_key}"
+        bucket = prepare_fake_s3(upload_key, upload)
 
-        s3_bucket.expects(:object).with("tombstone/original/1X/#{upload.sha1}.png").returns(s3_object)
-        expect_copy_from(s3_object, "s3-upload-bucket/original/1X/#{upload.sha1}.png")
-        s3_bucket.expects(:object).with("original/1X/#{upload.sha1}.png").returns(s3_object)
-        s3_object.expects(:delete)
+        upload.update!(url: "//s3-upload-bucket.s3.dualstack.us-west-1.amazonaws.com/#{upload_key}")
+
+        expect(bucket.find_object(upload_key)).to be_present
+        expect(bucket.find_object(tombstone_key)).to be_nil
 
         store.remove_upload(upload)
-      end
 
-      it "removes the optimized image from s3 with the right paths" do
-        optimized = Fabricate(:optimized_image, version: 1)
-        upload = optimized.upload
-        path = "optimized/1X/#{upload.sha1}_#{optimized.version}_#{optimized.width}x#{optimized.height}.png"
-
-        s3_helper.expects(:s3_bucket).returns(s3_bucket).at_least_once
-        optimized.update!(url: "//s3-upload-bucket.s3.dualstack.us-west-1.amazonaws.com/#{path}")
-        s3_object = stub
-
-        s3_bucket.expects(:object).with("tombstone/#{path}").returns(s3_object)
-        expect_copy_from(s3_object, "s3-upload-bucket/#{path}")
-        s3_bucket.expects(:object).with(path).returns(s3_object)
-        s3_object.expects(:delete)
-
-        store.remove_optimized_image(optimized)
+        expect(bucket.find_object(upload_key)).to be_nil
+        expect(bucket.find_object(tombstone_key)).to be_present
       end
 
       describe "when s3_upload_bucket includes folders path" do
@@ -249,41 +235,47 @@ describe FileStore::S3Store do
         end
 
         it "removes the file from s3 with the right paths" do
-          s3_helper.expects(:s3_bucket).returns(s3_bucket).at_least_once
-          upload.update!(url: "//s3-upload-bucket.s3.dualstack.us-west-1.amazonaws.com/discourse-uploads/original/1X/#{upload.sha1}.png")
-          s3_object = stub
+          upload_key = "discourse-uploads/#{Discourse.store.get_path_for_upload(upload)}"
+          tombstone_key = "discourse-uploads/tombstone/#{Discourse.store.get_path_for_upload(upload)}"
+          bucket = prepare_fake_s3(upload_key, upload)
 
-          s3_bucket.expects(:object).with("discourse-uploads/tombstone/original/1X/#{upload.sha1}.png").returns(s3_object)
-          expect_copy_from(s3_object, "s3-upload-bucket/discourse-uploads/original/1X/#{upload.sha1}.png")
-          s3_bucket.expects(:object).with("discourse-uploads/original/1X/#{upload.sha1}.png").returns(s3_object)
-          s3_object.expects(:delete)
+          upload.update!(url: "//s3-upload-bucket.s3.dualstack.us-west-1.amazonaws.com/#{upload_key}")
+
+          expect(bucket.find_object(upload_key)).to be_present
+          expect(bucket.find_object(tombstone_key)).to be_nil
 
           store.remove_upload(upload)
+
+          expect(bucket.find_object(upload_key)).to be_nil
+          expect(bucket.find_object(tombstone_key)).to be_present
         end
       end
     end
 
     describe "#remove_optimized_image" do
-      let(:image_path) do
-        FileStore::BaseStore.new.get_path_for_optimized_image(optimized_image)
-      end
+      let(:optimized_key)  { FileStore::BaseStore.new.get_path_for_optimized_image(optimized_image) }
+      let(:tombstone_key) { "tombstone/#{optimized_key}" }
+      let(:upload) { optimized_image.upload }
+      let(:upload_key) { Discourse.store.get_path_for_upload(upload) }
 
       before do
-        optimized_image.update!(
-          url: "//s3-upload-bucket.s3.dualstack.us-west-1.amazonaws.com/#{image_path}"
-        )
+        optimized_image.update!(url: "//s3-upload-bucket.s3.dualstack.us-west-1.amazonaws.com/#{optimized_key}")
+        upload.update!(url: "//s3-upload-bucket.s3.dualstack.us-west-1.amazonaws.com/#{upload_key}")
       end
 
-      it "removes the file from s3 with the right paths" do
-        s3_helper.expects(:s3_bucket).returns(s3_bucket).at_least_once
-        s3_object = stub
+      it "removes the optimized image from s3 with the right paths" do
+        bucket = prepare_fake_s3(upload_key, upload)
+        store_fake_s3_object(optimized_key, optimized_image)
 
-        s3_bucket.expects(:object).with("tombstone/#{image_path}").returns(s3_object)
-        expect_copy_from(s3_object, "s3-upload-bucket/#{image_path}")
-        s3_bucket.expects(:object).with("#{image_path}").returns(s3_object)
-        s3_object.expects(:delete)
+        expect(bucket.find_object(upload_key)).to be_present
+        expect(bucket.find_object(optimized_key)).to be_present
+        expect(bucket.find_object(tombstone_key)).to be_nil
 
         store.remove_optimized_image(optimized_image)
+
+        expect(bucket.find_object(upload_key)).to be_present
+        expect(bucket.find_object(optimized_key)).to be_nil
+        expect(bucket.find_object(tombstone_key)).to be_present
       end
 
       describe "when s3_upload_bucket includes folders path" do
@@ -291,29 +283,24 @@ describe FileStore::S3Store do
           SiteSetting.s3_upload_bucket = "s3-upload-bucket/discourse-uploads"
         end
 
-        before do
-          optimized_image.update!(
-            url: "//s3-upload-bucket.s3.dualstack.us-west-1.amazonaws.com/discourse-uploads/#{image_path}"
-          )
-        end
+        let(:image_path) { FileStore::BaseStore.new.get_path_for_optimized_image(optimized_image) }
+        let(:optimized_key)  { "discourse-uploads/#{image_path}"  }
+        let(:tombstone_key) { "discourse-uploads/tombstone/#{image_path}" }
+        let(:upload_key) { "discourse-uploads/#{Discourse.store.get_path_for_upload(upload)}" }
 
         it "removes the file from s3 with the right paths" do
-          s3_helper.expects(:s3_bucket).returns(s3_bucket).at_least_once
-          s3_object = stub
+          bucket = prepare_fake_s3(upload_key, upload)
+          store_fake_s3_object(optimized_key, optimized_image)
 
-          s3_bucket.expects(:object)
-            .with("discourse-uploads/tombstone/#{image_path}")
-            .returns(s3_object)
-
-          expect_copy_from(s3_object, "s3-upload-bucket/discourse-uploads/#{image_path}")
-
-          s3_bucket.expects(:object).with(
-            "discourse-uploads/#{image_path}"
-          ).returns(s3_object)
-
-          s3_object.expects(:delete)
+          expect(bucket.find_object(upload_key)).to be_present
+          expect(bucket.find_object(optimized_key)).to be_present
+          expect(bucket.find_object(tombstone_key)).to be_nil
 
           store.remove_optimized_image(optimized_image)
+
+          expect(bucket.find_object(upload_key)).to be_present
+          expect(bucket.find_object(optimized_key)).to be_nil
+          expect(bucket.find_object(tombstone_key)).to be_present
         end
       end
     end
@@ -484,11 +471,18 @@ describe FileStore::S3Store do
     end
   end
 
-  def expect_copy_from(s3_object, source)
-    s3_object.expects(:copy_from).with(
-      copy_source: source
-    ).returns(
-      stub(copy_object_result: stub(etag: '"etagtest"'))
+  def prepare_fake_s3(upload_key, upload)
+    @fake_s3 = FakeS3.create
+    @fake_s3_bucket = @fake_s3.bucket(SiteSetting.s3_upload_bucket)
+    store_fake_s3_object(upload_key, upload)
+    @fake_s3_bucket
+  end
+
+  def store_fake_s3_object(upload_key, upload)
+    @fake_s3_bucket.put_object(
+      key: upload_key,
+      size: upload.filesize,
+      last_modified: upload.created_at
     )
   end
 end
diff --git a/spec/multisite/s3_store_spec.rb b/spec/multisite/s3_store_spec.rb
index c0e66060e3..2429802424 100644
--- a/spec/multisite/s3_store_spec.rb
+++ b/spec/multisite/s3_store_spec.rb
@@ -99,61 +99,73 @@ RSpec.describe 'Multisite s3 uploads', type: :multisite do
 
     describe "#remove_upload" do
       let(:store) { FileStore::S3Store.new }
-      let(:client) { Aws::S3::Client.new(stub_responses: true) }
-      let(:resource) { Aws::S3::Resource.new(client: client) }
-      let(:s3_bucket) { resource.bucket(SiteSetting.s3_upload_bucket) }
-      let(:s3_helper) { store.s3_helper }
+
+      let(:upload) { build_upload }
+      let(:upload_key) { "#{upload_path}/original/1X/#{upload.sha1}.png" }
+
+      def prepare_fake_s3
+        @fake_s3 = FakeS3.create
+        bucket = @fake_s3.bucket(SiteSetting.s3_upload_bucket)
+        bucket.put_object(
+          key: upload_key,
+          size: upload.filesize,
+          last_modified: upload.created_at
+        )
+        bucket
+      end
 
       it "removes the file from s3 on multisite" do
         test_multisite_connection('default') do
-          upload = build_upload
-          s3_helper.expects(:s3_bucket).returns(s3_bucket).at_least_once
           upload.update!(url: "//s3-upload-bucket.s3.dualstack.us-west-1.amazonaws.com/#{upload_path}/original/1X/#{upload.sha1}.png")
-          s3_object = stub
+          tombstone_key = "uploads/tombstone/default/original/1X/#{upload.sha1}.png"
+          bucket = prepare_fake_s3
 
-          s3_bucket.expects(:object).with("uploads/tombstone/default/original/1X/#{upload.sha1}.png").returns(s3_object)
-          expect_copy_from(s3_object, "s3-upload-bucket/#{upload_path}/original/1X/#{upload.sha1}.png")
-          s3_bucket.expects(:object).with("#{upload_path}/original/1X/#{upload.sha1}.png").returns(s3_object)
-          s3_object.expects(:delete)
+          expect(bucket.find_object(upload_key)).to be_present
+          expect(bucket.find_object(tombstone_key)).to be_nil
 
           store.remove_upload(upload)
+
+          expect(bucket.find_object(upload_key)).to be_nil
+          expect(bucket.find_object(tombstone_key)).to be_present
         end
       end
 
       it "removes the file from s3 on another multisite db" do
         test_multisite_connection('second') do
-          upload = build_upload
-          s3_helper.expects(:s3_bucket).returns(s3_bucket).at_least_once
           upload.update!(url: "//s3-upload-bucket.s3.dualstack.us-west-1.amazonaws.com/#{upload_path}/original/1X/#{upload.sha1}.png")
-          s3_object = stub
+          tombstone_key = "uploads/tombstone/second/original/1X/#{upload.sha1}.png"
+          bucket = prepare_fake_s3
 
-          s3_bucket.expects(:object).with("uploads/tombstone/second/original/1X/#{upload.sha1}.png").returns(s3_object)
-          expect_copy_from(s3_object, "s3-upload-bucket/#{upload_path}/original/1X/#{upload.sha1}.png")
-          s3_bucket.expects(:object).with("#{upload_path}/original/1X/#{upload.sha1}.png").returns(s3_object)
-          s3_object.expects(:delete)
+          expect(bucket.find_object(upload_key)).to be_present
+          expect(bucket.find_object(tombstone_key)).to be_nil
 
           store.remove_upload(upload)
+
+          expect(bucket.find_object(upload_key)).to be_nil
+          expect(bucket.find_object(tombstone_key)).to be_present
         end
       end
 
       describe "when s3_upload_bucket includes folders path" do
+        let(:upload_key) { "discourse-uploads/#{upload_path}/original/1X/#{upload.sha1}.png" }
+
         before do
           SiteSetting.s3_upload_bucket = "s3-upload-bucket/discourse-uploads"
         end
 
         it "removes the file from s3 on multisite" do
           test_multisite_connection('default') do
-            upload = build_upload
-            s3_helper.expects(:s3_bucket).returns(s3_bucket).at_least_once
             upload.update!(url: "//s3-upload-bucket.s3.dualstack.us-west-1.amazonaws.com/discourse-uploads/#{upload_path}/original/1X/#{upload.sha1}.png")
-            s3_object = stub
+            tombstone_key = "discourse-uploads/uploads/tombstone/default/original/1X/#{upload.sha1}.png"
+            bucket = prepare_fake_s3
 
-            s3_bucket.expects(:object).with("discourse-uploads/uploads/tombstone/default/original/1X/#{upload.sha1}.png").returns(s3_object)
-            expect_copy_from(s3_object, "s3-upload-bucket/discourse-uploads/#{upload_path}/original/1X/#{upload.sha1}.png")
-            s3_bucket.expects(:object).with("discourse-uploads/#{upload_path}/original/1X/#{upload.sha1}.png").returns(s3_object)
-            s3_object.expects(:delete)
+            expect(bucket.find_object(upload_key)).to be_present
+            expect(bucket.find_object(tombstone_key)).to be_nil
 
             store.remove_upload(upload)
+
+            expect(bucket.find_object(upload_key)).to be_nil
+            expect(bucket.find_object(tombstone_key)).to be_present
           end
         end
       end
@@ -345,12 +357,4 @@ RSpec.describe 'Multisite s3 uploads', type: :multisite do
       end
     end
   end
-
-  def expect_copy_from(s3_object, source)
-    s3_object.expects(:copy_from).with(
-      copy_source: source
-    ).returns(
-      stub(copy_object_result: stub(etag: '"etagtest"'))
-    )
-  end
 end
diff --git a/spec/services/external_upload_manager_spec.rb b/spec/services/external_upload_manager_spec.rb
index aa9e31969c..6a0332ea18 100644
--- a/spec/services/external_upload_manager_spec.rb
+++ b/spec/services/external_upload_manager_spec.rb
@@ -2,7 +2,6 @@
 
 RSpec.describe ExternalUploadManager do
   fab!(:user) { Fabricate(:user) }
-  let(:type) { "card_background" }
   let!(:logo_file) { file_from_fixtures("logo.png") }
   let!(:pdf_file) { file_from_fixtures("large.pdf", "pdf") }
   let(:object_size) { 1.megabyte }
@@ -10,9 +9,9 @@ RSpec.describe ExternalUploadManager do
   let(:client_sha1) { Upload.generate_digest(object_file) }
   let(:sha1) { Upload.generate_digest(object_file) }
   let(:object_file) { logo_file }
-  let(:metadata_headers) { {} }
+  let(:external_upload_stub_metadata) { {} }
   let!(:external_upload_stub) { Fabricate(:image_external_upload_stub, created_by: user) }
-  let(:upload_base_url) { "https://#{SiteSetting.s3_upload_bucket}.s3.#{SiteSetting.s3_region}.amazonaws.com" }
+  let(:s3_bucket_name) { SiteSetting.s3_upload_bucket }
 
   subject do
     ExternalUploadManager.new(external_upload_stub)
@@ -27,10 +26,8 @@ RSpec.describe ExternalUploadManager do
     SiteSetting.s3_backup_bucket = "s3-backup-bucket"
     SiteSetting.backup_location = BackupLocationSiteSetting::S3
 
-    stub_head_object
+    prepare_fake_s3
     stub_download_object_filehelper
-    stub_copy_object
-    stub_delete_object
   end
 
   describe "#ban_user_from_external_uploads!" do
@@ -69,6 +66,7 @@ RSpec.describe ExternalUploadManager do
         before do
           external_upload_stub.update!(status: ExternalUploadStub.statuses[:uploaded])
         end
+
         it "raises an error" do
           expect { subject.transform! }.to raise_error(ExternalUploadManager::CannotPromoteError)
         end
@@ -77,14 +75,11 @@ RSpec.describe ExternalUploadManager do
       context "when the upload does not get changed in UploadCreator (resized etc.)" do
         it "copies the stubbed upload on S3 to its new destination and deletes it" do
           upload = subject.transform!
-          expect(WebMock).to have_requested(
-            :put,
-            "#{upload_base_url}/#{Discourse.store.get_path_for_upload(upload)}",
-          ).with(headers: { 'X-Amz-Copy-Source' => "#{SiteSetting.s3_upload_bucket}/#{external_upload_stub.key}" })
-          expect(WebMock).to have_requested(
-            :delete,
-            "#{upload_base_url}/#{external_upload_stub.key}"
-          )
+
+          bucket = @fake_s3.bucket(SiteSetting.s3_upload_bucket)
+          expect(@fake_s3.operation_called?(:copy_object)).to eq(true)
+          expect(bucket.find_object(Discourse.store.get_path_for_upload(upload))).to be_present
+          expect(bucket.find_object(external_upload_stub.key)).to be_nil
         end
 
         it "errors if the image upload is too big" do
@@ -105,22 +100,22 @@ RSpec.describe ExternalUploadManager do
       end
 
       context "when the upload does get changed by the UploadCreator" do
-        let(:file) { file_from_fixtures("should_be_jpeg.heic", "images") }
+        let(:object_file) { file_from_fixtures("should_be_jpeg.heic", "images") }
+        let(:object_size) { 1.megabyte }
+        let(:external_upload_stub) { Fabricate(:image_external_upload_stub, original_filename: "should_be_jpeg.heic", filesize: object_size) }
 
         it "creates a new upload in s3 (not copy) and deletes the original stubbed upload" do
           upload = subject.transform!
-          expect(WebMock).to have_requested(
-            :put,
-            "#{upload_base_url}/#{Discourse.store.get_path_for_upload(upload)}",
-          )
-          expect(WebMock).to have_requested(
-            :delete, "#{upload_base_url}/#{external_upload_stub.key}"
-          )
+
+          bucket = @fake_s3.bucket(SiteSetting.s3_upload_bucket)
+          expect(@fake_s3.operation_called?(:copy_object)).to eq(false)
+          expect(bucket.find_object(Discourse.store.get_path_for_upload(upload))).to be_present
+          expect(bucket.find_object(external_upload_stub.key)).to be_nil
         end
       end
 
       context "when the sha has been set on the s3 object metadata by the clientside JS" do
-        let(:metadata_headers) { { "x-amz-meta-sha1-checksum" => client_sha1 } }
+        let(:external_upload_stub_metadata) { { "sha1-checksum" => client_sha1 } }
 
         context "when the downloaded file sha1 does not match the client sha1" do
           let(:client_sha1) { "blahblah" }
@@ -128,6 +123,9 @@ RSpec.describe ExternalUploadManager do
           it "raises an error, deletes the stub" do
             expect { subject.transform! }.to raise_error(ExternalUploadManager::ChecksumMismatchError)
             expect(ExternalUploadStub.exists?(id: external_upload_stub.id)).to eq(false)
+
+            bucket = @fake_s3.bucket(SiteSetting.s3_upload_bucket)
+            expect(bucket.find_object(external_upload_stub.key)).to be_nil
           end
 
           it "does not delete the stub if enable_upload_debug_mode" do
@@ -135,6 +133,9 @@ RSpec.describe ExternalUploadManager do
             expect { subject.transform! }.to raise_error(ExternalUploadManager::ChecksumMismatchError)
             external_stub = ExternalUploadStub.find(external_upload_stub.id)
             expect(external_stub.status).to eq(ExternalUploadStub.statuses[:failed])
+
+            bucket = @fake_s3.bucket(SiteSetting.s3_upload_bucket)
+            expect(bucket.find_object(external_upload_stub.key)).to be_present
           end
         end
       end
@@ -150,10 +151,9 @@ RSpec.describe ExternalUploadManager do
           expect { subject.transform! }.to raise_error(ExternalUploadManager::SizeMismatchError)
           expect(ExternalUploadStub.exists?(id: external_upload_stub.id)).to eq(false)
           expect(Discourse.redis.get("#{ExternalUploadManager::BAN_USER_REDIS_PREFIX}#{external_upload_stub.created_by_id}")).to eq("1")
-          expect(WebMock).to have_requested(
-            :delete,
-            "#{upload_base_url}/#{external_upload_stub.key}"
-          )
+
+          bucket = @fake_s3.bucket(SiteSetting.s3_upload_bucket)
+          expect(bucket.find_object(external_upload_stub.key)).to be_nil
         end
 
         it "does not delete the stub if enable_upload_debug_mode" do
@@ -161,6 +161,9 @@ RSpec.describe ExternalUploadManager do
           expect { subject.transform! }.to raise_error(ExternalUploadManager::SizeMismatchError)
           external_stub = ExternalUploadStub.find(external_upload_stub.id)
           expect(external_stub.status).to eq(ExternalUploadStub.statuses[:failed])
+
+          bucket = @fake_s3.bucket(SiteSetting.s3_upload_bucket)
+          expect(bucket.find_object(external_upload_stub.key)).to be_present
         end
       end
     end
@@ -193,18 +196,14 @@ RSpec.describe ExternalUploadManager do
 
       it "copies the stubbed upload on S3 to its new destination and deletes it" do
         upload = subject.transform!
-        expect(WebMock).to have_requested(
-          :put,
-            "#{upload_base_url}/#{Discourse.store.get_path_for_upload(upload)}",
-        ).with(headers: { 'X-Amz-Copy-Source' => "#{SiteSetting.s3_upload_bucket}/#{external_upload_stub.key}" })
-        expect(WebMock).to have_requested(
-          :delete, "#{upload_base_url}/#{external_upload_stub.key}"
-        )
+
+        bucket = @fake_s3.bucket(SiteSetting.s3_upload_bucket)
+        expect(bucket.find_object(Discourse.store.get_path_for_upload(upload))).to be_present
+        expect(bucket.find_object(external_upload_stub.key)).to be_nil
       end
     end
 
     context "when the upload type is backup" do
-      let(:upload_base_url) { "https://#{SiteSetting.s3_backup_bucket}.s3.#{SiteSetting.s3_region}.amazonaws.com" }
       let(:object_size) { 200.megabytes }
       let(:object_file) { file_from_fixtures("backup_since_v1.6.tar.gz", "backups") }
       let!(:external_upload_stub) do
@@ -217,21 +216,7 @@ RSpec.describe ExternalUploadManager do
           folder_prefix: RailsMultisite::ConnectionManagement.current_db
         )
       end
-
-      before do
-        stub_request(:head, "https://#{SiteSetting.s3_backup_bucket}.s3.#{SiteSetting.s3_region}.amazonaws.com/")
-
-        # stub copy and delete object for backup, which copies the original filename to the root,
-        # and also uses current_db in the bucket name always
-        stub_request(
-          :put,
-          "#{upload_base_url}/#{RailsMultisite::ConnectionManagement.current_db}/backup_since_v1.6.tar.gz"
-        ).to_return(
-          status: 200,
-          headers: { "ETag" => etag },
-          body: copy_object_result
-        )
-      end
+      let(:s3_bucket_name) { SiteSetting.s3_backup_bucket }
 
       it "does not try and download the file" do
         FileHelper.expects(:download).never
@@ -253,32 +238,17 @@ RSpec.describe ExternalUploadManager do
       end
 
       it "copies the stubbed upload on S3 to its new destination and deletes it" do
-        upload = subject.transform!
-        expect(WebMock).to have_requested(
-          :put,
-          "#{upload_base_url}/#{RailsMultisite::ConnectionManagement.current_db}/backup_since_v1.6.tar.gz",
-        ).with(headers: { 'X-Amz-Copy-Source' => "#{SiteSetting.s3_backup_bucket}/#{external_upload_stub.key}" })
-        expect(WebMock).to have_requested(
-          :delete, "#{upload_base_url}/#{external_upload_stub.key}"
-        )
+        bucket = @fake_s3.bucket(SiteSetting.s3_backup_bucket)
+        expect(bucket.find_object(external_upload_stub.key)).to be_present
+
+        subject.transform!
+
+        expect(bucket.find_object("#{RailsMultisite::ConnectionManagement.current_db}/backup_since_v1.6.tar.gz")).to be_present
+        expect(bucket.find_object(external_upload_stub.key)).to be_nil
       end
     end
   end
 
-  def stub_head_object
-    stub_request(
-      :head,
-      "#{upload_base_url}/#{external_upload_stub.key}"
-    ).to_return(
-      status: 200,
-      headers: {
-        ETag: etag,
-        "Content-Length" => object_size,
-        "Content-Type" => "image/png",
-      }.merge(metadata_headers)
-    )
-  end
-
   def stub_download_object_filehelper
     signed_url = Discourse.store.signed_url_for_path(external_upload_stub.key)
     uri = URI.parse(signed_url)
@@ -289,49 +259,14 @@ RSpec.describe ExternalUploadManager do
     )
   end
 
-  def copy_object_result
-    <<~XML
-    <?xml version=\"1.0\" encoding=\"UTF-8\"?>\n
-    <CopyObjectResult
-      xmlns=\"http://s3.amazonaws.com/doc/2006-03-01/\">
-      <LastModified>2021-07-19T04:10:41.000Z</LastModified>
-      <ETag>&quot;#{etag}&quot;</ETag>
-    </CopyObjectResult>
-    XML
-  end
+  def prepare_fake_s3
+    @fake_s3 = FakeS3.create
 
-  def stub_copy_object
-    upload_pdf = Fabricate(:upload, sha1: "testbc60eb18e8f974cbfae8bb0f069c3a311024", original_filename: "test.pdf", extension: "pdf")
-    upload_path = Discourse.store.get_path_for_upload(upload_pdf)
-    upload_pdf.destroy!
-
-    stub_request(
-      :put,
-      "#{upload_base_url}/#{upload_path}"
-    ).to_return(
-      status: 200,
-      headers: { "ETag" => etag },
-      body: copy_object_result
-    )
-
-    upload_png = Fabricate(:upload, sha1: "bc975735dfc6409c1c2aa5ebf2239949bcbdbd65", original_filename: "test.png", extension: "png")
-    upload_path = Discourse.store.get_path_for_upload(upload_png)
-    upload_png.destroy!
-    stub_request(
-      :put,
-      "#{upload_base_url}/#{upload_path}"
-    ).to_return(
-      status: 200,
-      headers: { "ETag" => etag },
-      body: copy_object_result
-    )
-  end
-
-  def stub_delete_object
-    stub_request(
-      :delete, "#{upload_base_url}/#{external_upload_stub.key}"
-    ).to_return(
-      status: 200
+    @fake_s3.bucket(s3_bucket_name).put_object(
+      key: external_upload_stub.key,
+      size: object_size,
+      last_modified: Time.zone.now,
+      metadata: external_upload_stub_metadata
     )
   end
 end
diff --git a/spec/support/fake_s3.rb b/spec/support/fake_s3.rb
new file mode 100644
index 0000000000..48be026966
--- /dev/null
+++ b/spec/support/fake_s3.rb
@@ -0,0 +1,157 @@
+# frozen_string_literal: true
+
+class FakeS3
+  attr_reader :s3_client
+
+  def self.create
+    s3 = self.new
+    s3.stub_bucket(SiteSetting.s3_upload_bucket) if SiteSetting.s3_upload_bucket.present?
+    s3.stub_bucket(File.join(SiteSetting.s3_backup_bucket, RailsMultisite::ConnectionManagement.current_db)) if SiteSetting.s3_backup_bucket.present?
+    s3.stub_s3_helper
+    s3
+  end
+
+  def initialize
+    @buckets = {}
+    @operations = []
+    @s3_client = Aws::S3::Client.new(stub_responses: true, region: SiteSetting.s3_region)
+
+    stub_methods
+  end
+
+  def bucket(bucket_name)
+    bucket_name, _prefix = bucket_name.split("/", 2)
+    @buckets[bucket_name]
+  end
+
+  def stub_bucket(full_bucket_name)
+    bucket_name, _prefix = full_bucket_name.split("/", 2)
+
+    s3_helper = S3Helper.new(
+      full_bucket_name,
+      Rails.configuration.multisite ? FileStore::S3Store.new.multisite_tombstone_prefix : FileStore::S3Store::TOMBSTONE_PREFIX,
+      client: @s3_client
+    )
+    @buckets[bucket_name] = FakeS3Bucket.new(full_bucket_name, s3_helper)
+  end
+
+  def stub_s3_helper
+    @buckets.each do |bucket_name, bucket|
+      S3Helper.stubs(:new)
+        .with { |b| b == bucket_name || b == bucket.name }
+        .returns(bucket.s3_helper)
+    end
+  end
+
+  def operation_called?(name)
+    @operations.any? do |operation|
+      operation[:name] == name && (block_given? ? yield(operation) : true)
+    end
+  end
+
+  private
+
+  def find_bucket(params)
+    bucket(params[:bucket])
+  end
+
+  def find_object(params)
+    bucket = find_bucket(params)
+    bucket&.find_object(params[:key])
+  end
+
+  def log_operation(context)
+    @operations << {
+      name: context.operation_name,
+      params: context.params.dup
+    }
+  end
+
+  def calculate_etag(context)
+    # simple, reproducible ETag calculation
+    Digest::MD5.hexdigest(context.params.to_json)
+  end
+
+  def stub_methods
+    @s3_client.stub_responses(:head_object, -> (context) do
+      log_operation(context)
+
+      if object = find_object(context.params)
+        { content_length: object[:size], last_modified: object[:last_modified], metadata: object[:metadata] }
+      else
+        { status_code: 404, headers: {}, body: "" }
+      end
+    end)
+
+    @s3_client.stub_responses(:get_object, -> (context) do
+      log_operation(context)
+
+      if object = find_object(context.params)
+        { content_length: object[:size], body: "" }
+      else
+        { status_code: 404, headers: {}, body: "" }
+      end
+    end)
+
+    @s3_client.stub_responses(:delete_object, -> (context) do
+      log_operation(context)
+
+      find_bucket(context.params)&.delete_object(context.params[:key])
+      nil
+    end)
+
+    @s3_client.stub_responses(:copy_object, -> (context) do
+      log_operation(context)
+
+      source_bucket_name, source_key = context.params[:copy_source].split("/", 2)
+      copy_source = { bucket: source_bucket_name, key: source_key }
+
+      if context.params[:metadata_directive] == "REPLACE"
+        attribute_overrides = context.params.except(:copy_source, :metadata_directive)
+      else
+        attribute_overrides = context.params.slice(:key, :bucket)
+      end
+
+      new_object = find_object(copy_source).dup.merge(attribute_overrides)
+      find_bucket(new_object).put_object(new_object)
+
+      { copy_object_result: { etag: calculate_etag(context) } }
+    end)
+
+    @s3_client.stub_responses(:create_multipart_upload, -> (context) do
+      log_operation(context)
+
+      find_bucket(context.params).put_object(context.params)
+      { upload_id: SecureRandom.hex }
+    end)
+
+    @s3_client.stub_responses(:put_object, -> (context) do
+      log_operation(context)
+
+      find_bucket(context.params).put_object(context.params)
+      { etag: calculate_etag(context) }
+    end)
+  end
+end
+
+class FakeS3Bucket
+  attr_reader :name, :s3_helper
+
+  def initialize(bucket_name, s3_helper)
+    @name = bucket_name
+    @s3_helper = s3_helper
+    @objects = {}
+  end
+
+  def put_object(obj)
+    @objects[obj[:key]] = obj
+  end
+
+  def delete_object(key)
+    @objects.delete(key)
+  end
+
+  def find_object(key)
+    @objects[key]
+  end
+end