diff --git a/spec/lib/gitlab/background_migration/normalize_ldap_extern_uids_range_spec.rb b/spec/lib/gitlab/background_migration/normalize_ldap_extern_uids_range_spec.rb
new file mode 100644
index 00000000000..dfbf1bb681a
--- /dev/null
+++ b/spec/lib/gitlab/background_migration/normalize_ldap_extern_uids_range_spec.rb
@@ -0,0 +1,36 @@
+require 'spec_helper'
+
+describe Gitlab::BackgroundMigration::NormalizeLdapExternUidsRange, :migration, schema: 20170921101004 do
+  let!(:identities) { table(:identities) }
+
+  before do
+    # LDAP identities
+    (1..4).each do |i|
+      identities.create!(id: i, provider: 'ldapmain', extern_uid: " uid = foo #{i}, ou = People, dc = example, dc = com ", user_id: i)
+    end
+
+    # Non-LDAP identity
+    identities.create!(id: 5, provider: 'foo', extern_uid: " uid = foo 5, ou = People, dc = example, dc = com ", user_id: 5)
+
+    # Another LDAP identity
+    identities.create!(id: 6, provider: 'ldapmain', extern_uid: " uid = foo 6, ou = People, dc = example, dc = com ", user_id: 6)
+  end
+
+  it 'normalizes the LDAP identities in the range' do
+    described_class.new.perform(1, 3)
+    expect(identities.find(1).extern_uid).to eq("uid=foo 1,ou=people,dc=example,dc=com")
+    expect(identities.find(2).extern_uid).to eq("uid=foo 2,ou=people,dc=example,dc=com")
+    expect(identities.find(3).extern_uid).to eq("uid=foo 3,ou=people,dc=example,dc=com")
+    expect(identities.find(4).extern_uid).to eq(" uid = foo 4, ou = People, dc = example, dc = com ")
+    expect(identities.find(5).extern_uid).to eq(" uid = foo 5, ou = People, dc = example, dc = com ")
+    expect(identities.find(6).extern_uid).to eq(" uid = foo 6, ou = People, dc = example, dc = com ")
+
+    described_class.new.perform(4, 6)
+    expect(identities.find(1).extern_uid).to eq("uid=foo 1,ou=people,dc=example,dc=com")
+    expect(identities.find(2).extern_uid).to eq("uid=foo 2,ou=people,dc=example,dc=com")
+    expect(identities.find(3).extern_uid).to eq("uid=foo 3,ou=people,dc=example,dc=com")
+    expect(identities.find(4).extern_uid).to eq("uid=foo 4,ou=people,dc=example,dc=com")
+    expect(identities.find(5).extern_uid).to eq(" uid = foo 5, ou = People, dc = example, dc = com ")
+    expect(identities.find(6).extern_uid).to eq("uid=foo 6,ou=people,dc=example,dc=com")
+  end
+end
diff --git a/spec/migrations/normalize_ldap_extern_uids_spec.rb b/spec/migrations/normalize_ldap_extern_uids_spec.rb
new file mode 100644
index 00000000000..262d7742aaf
--- /dev/null
+++ b/spec/migrations/normalize_ldap_extern_uids_spec.rb
@@ -0,0 +1,56 @@
+require 'spec_helper'
+require Rails.root.join('db', 'post_migrate', '20170921101004_normalize_ldap_extern_uids')
+
+describe NormalizeLdapExternUids, :migration, :sidekiq do
+  let!(:identities) { table(:identities) }
+
+  around do |example|
+    Timecop.freeze { example.run }
+  end
+
+  before do
+    stub_const("Gitlab::Database::MigrationHelpers::BACKGROUND_MIGRATION_BATCH_SIZE", 2)
+    stub_const("Gitlab::Database::MigrationHelpers::BACKGROUND_MIGRATION_JOB_BUFFER_SIZE", 2)
+
+    # LDAP identities
+    (1..4).each do |i|
+      identities.create!(id: i, provider: 'ldapmain', extern_uid: " uid = foo #{i}, ou = People, dc = example, dc = com ", user_id: i)
+    end
+
+    # Non-LDAP identity
+    identities.create!(id: 5, provider: 'foo', extern_uid: " uid = foo 5, ou = People, dc = example, dc = com ", user_id: 5)
+  end
+
+  it 'correctly schedules background migrations' do
+    Sidekiq::Testing.fake! do
+      Timecop.freeze do
+        migrate!
+
+        expect(BackgroundMigrationWorker.jobs[0]['args']).to eq([described_class::MIGRATION, [1, 2]])
+        expect(BackgroundMigrationWorker.jobs[0]['at']).to eq(10.seconds.from_now.to_f)
+        expect(BackgroundMigrationWorker.jobs[1]['args']).to eq([described_class::MIGRATION, [3, 4]])
+        expect(BackgroundMigrationWorker.jobs[1]['at']).to eq(20.seconds.from_now.to_f)
+        expect(BackgroundMigrationWorker.jobs[2]['args']).to eq([described_class::MIGRATION, [5, 5]])
+        expect(BackgroundMigrationWorker.jobs[2]['at']).to eq(30.seconds.from_now.to_f)
+        expect(BackgroundMigrationWorker.jobs.size).to eq 3
+      end
+    end
+  end
+
+  it 'migrates the LDAP identities' do
+    Sidekiq::Testing.inline! do
+      migrate!
+      identities.where(id: 1..4).each do |identity|
+        expect(identity.extern_uid).to eq("uid=foo #{identity.id},ou=people,dc=example,dc=com")
+      end
+    end
+  end
+
+  it 'does not modify non-LDAP identities' do
+    Sidekiq::Testing.inline! do
+      migrate!
+      identity = identities.last
+      expect(identity.extern_uid).to eq(" uid = foo 5, ou = People, dc = example, dc = com ")
+    end
+  end
+end