Preserve `up` and `down` return type

In Rails 4.2 calling `ActiveRecord::Migrator.migrate` would return an array of results. Without realizing that this return type was expected I accidentally introduced a change in https://github.com/rails/rails/commit/4d60e93174a3d6d90b1a06fc7515cb5cd749a6f3

This PR preserves the previous behavior and adds a test on the return type. This will need a backport to 5.0 branch.

1 files changed, 14 insertions, 0 deletions

diff --git a/activerecord/test/cases/migrator_test.rb b/activerecord/test/cases/migrator_test.rb
index bb9835394b..cb44c443c7 100644
--- a/activerecord/test/cases/migrator_test.rb
+++ b/activerecord/test/cases/migrator_test.rb
@@ -290,6 +290,20 @@ class MigratorTest < ActiveRecord::TestCase
     assert_equal [[:up, 1], [:up, 2], [:up, 3]], calls
   end
 
+  def test_migrator_output
+    _, migrator = migrator_class(3)
+
+    result = migrator.migrate("valid")
+    assert_equal(3, result.count)
+
+    # Nothing migrated from duplicate run
+    result = migrator.migrate("valid")
+    assert_equal(0, result.count)
+
+    result = migrator.rollback("valid")
+    assert_equal(1, result.count)
+  end
+
   def test_migrator_rollback
     _, migrator = migrator_class(3)