Sync test DB from schema using its SHA1

activerecord/lib/active_record/migration.rb

@@ -587,18 +587,22 @@ def check_pending!(connection = Base.connection)
       end
 
       def load_schema_if_pending!
-        if Base.connection.migration_context.needs_migration? || !Base.connection.migration_context.any_migrations?
+        current_config = Base.connection_config
+        all_configs = ActiveRecord::Base.configurations.configs_for(env_name: Rails.env)
+
+        unless all_configs.all? { |config| Tasks::DatabaseTasks.schema_up_to_date?(config.config) }
           # Roundtrip to Rake to allow plugins to hook into database initialization.
           root = defined?(ENGINE_ROOT) ? ENGINE_ROOT : Rails.root
           FileUtils.cd(root) do
-            current_config = Base.connection_config
             Base.clear_all_connections!
             system("bin/rails db:test:prepare")
-            # Establish a new connection, the old database may be gone (db:test:prepare uses purge)
-            Base.establish_connection(current_config)
           end
-          check_pending!
         end
+
+        # Establish a new connection, the old database may be gone (db:test:prepare uses purge)
+        Base.establish_connection(current_config)
+
+        check_pending!
       end
 
       def maintain_test_schema! #:nodoc:

activerecord/lib/active_record/tasks/database_tasks.rb

@@ -332,10 +332,21 @@ def load_schema(configuration, format = ActiveRecord::Base.schema_format, file =
         end
         ActiveRecord::InternalMetadata.create_table
         ActiveRecord::InternalMetadata[:environment] = environment
+        ActiveRecord::InternalMetadata[:schema_sha1] = schema_sha1(file)
       ensure
         Migration.verbose = verbose_was
       end
 
+      def schema_up_to_date?(configuration, format = ActiveRecord::Base.schema_format, file = nil, environment = env, spec_name = "primary")
+        file ||= dump_filename(spec_name, format)
+
+        return true unless File.exist?(file)
+
+        ActiveRecord::Base.establish_connection(configuration)
+        return false unless ActiveRecord::InternalMetadata.table_exists?
+        ActiveRecord::InternalMetadata[:schema_sha1] == schema_sha1(file)
+      end
+
       def dump_schema(configuration, format = ActiveRecord::Base.schema_format, spec_name = "primary") # :nodoc:
         require "active_record/schema_dumper"
         filename = dump_filename(spec_name, format)
@@ -467,6 +478,10 @@ def each_local_configuration
         def local_database?(configuration)
           configuration["host"].blank? || LOCAL_HOSTS.include?(configuration["host"])
         end
+
+        def schema_sha1(file)
+          Digest::SHA1.hexdigest(File.read(file))
+        end
     end
   end
 end

railties/test/application/test_test.rb

@@ -232,10 +232,7 @@ class UserTest < ActiveSupport::TestCase
       assert_successful_test_run("models/user_test.rb")
     end
 
-    # TODO: would be nice if we could detect the schema change automatically.
-    # For now, the user has to synchronize the schema manually.
-    # This test case serves as a reminder for this use case.
-    test "manually synchronize test schema after rollback" do
+    test "automatically synchronizes test schema after rollback" do
       output  = rails("generate", "model", "user", "name:string")
       version = output.match(/(\d+)_create_users\.rb/)[1]
 
@@ -268,10 +265,6 @@ class UserTest < ActiveSupport::TestCase
         end
       RUBY
 
-      assert_successful_test_run "models/user_test.rb"
-
-      rails "db:test:prepare"
-
       assert_unsuccessful_run "models/user_test.rb", <<-ASSERTION
 Expected: ["id", "name"]
   Actual: ["id", "name", "age"]