Add assertions for ActiveRecord::Base.current_role

Since the `current_role` is public API.

activerecord/test/cases/connection_adapters/connection_handlers_multi_db_test.rb

@@ -108,6 +108,7 @@ def test_switching_connections_via_handler
           ActiveRecord::Base.connected_to(role: :reading) do
             @ro_handler = ActiveRecord::Base.connection_handler
             assert_equal ActiveRecord::Base.connection_handler, ActiveRecord::Base.connection_handlers[:reading]
+            assert_equal :reading, ActiveRecord::Base.current_role
             assert ActiveRecord::Base.connected_to?(role: :reading)
             assert_not ActiveRecord::Base.connected_to?(role: :writing)
           end
@@ -115,6 +116,7 @@ def test_switching_connections_via_handler
           ActiveRecord::Base.connected_to(role: :writing) do
             assert_equal ActiveRecord::Base.connection_handler, ActiveRecord::Base.connection_handlers[:writing]
             assert_not_equal @ro_handler, ActiveRecord::Base.connection_handler
+            assert_equal :writing, ActiveRecord::Base.current_role
             assert ActiveRecord::Base.connected_to?(role: :writing)
             assert_not ActiveRecord::Base.connected_to?(role: :reading)
           end
@@ -129,6 +131,7 @@ def test_switching_connections_with_database_url
           previous_url, ENV["DATABASE_URL"] = ENV["DATABASE_URL"], "postgres://localhost/foo"
 
           ActiveRecord::Base.connected_to(database: { writing: "postgres://localhost/bar" }) do
+            assert_equal :writing, ActiveRecord::Base.current_role
             assert ActiveRecord::Base.connected_to?(role: :writing)
 
             handler = ActiveRecord::Base.connection_handler
@@ -148,6 +151,7 @@ def test_switching_connections_with_database_config_hash
           config = { adapter: "sqlite3", database: "db/readonly.sqlite3" }
 
           ActiveRecord::Base.connected_to(database: { writing: config }) do
+            assert_equal :writing, ActiveRecord::Base.current_role
             assert ActiveRecord::Base.connected_to?(role: :writing)
 
             handler = ActiveRecord::Base.connection_handler
@@ -187,6 +191,7 @@ def test_switching_connections_with_database_symbol
           @prev_configs, ActiveRecord::Base.configurations = ActiveRecord::Base.configurations, config
 
           ActiveRecord::Base.connected_to(database: :readonly) do
+            assert_equal :readonly, ActiveRecord::Base.current_role
             assert ActiveRecord::Base.connected_to?(role: :readonly)
 
             handler = ActiveRecord::Base.connection_handler
@@ -211,6 +216,7 @@ def test_connects_to_with_single_configuration
 
           assert_equal 1, ActiveRecord::Base.connection_handlers.size
           assert_equal ActiveRecord::Base.connection_handler, ActiveRecord::Base.connection_handlers[:writing]
+          assert_equal :writing, ActiveRecord::Base.current_role
           assert ActiveRecord::Base.connected_to?(role: :writing)
         ensure
           ActiveRecord::Base.configurations = @prev_configs