Fix various tests (#333)

- Remove `database_exists?` method from `CockroachDBAdapter`, the
  original method is fine.
- Exclude a test that will be fixed in Rails 7.2

Gemfile

@@ -62,7 +62,6 @@ group :development, :test do
 
   # Gems used by the ActiveRecord test suite
   gem "bcrypt", "~> 3.1.18"
-  gem "mocha", "~> 1.14.0"
   gem "sqlite3", "~> 1.4.4"
 
   gem "minitest", "~> 5.15.0"

lib/active_record/connection_adapters/cockroachdb_adapter.rb

@@ -243,12 +243,6 @@ def supports_deferrable_constraints?
       #     @crdb_version = version_num.to_i
       #   end
 
-      def self.database_exists?(config)
-        !!ActiveRecord::Base.cockroachdb_connection(config)
-      rescue ActiveRecord::NoDatabaseError
-        false
-      end
-
       def initialize(...)
         super
 

test/cases/connection_adapters/type_test.rb

@@ -7,10 +7,9 @@ module CockroachDB
   module ConnectionAdapters
     class TypeTest < ActiveRecord::TestCase
       fixtures :accounts
-      class SqliteModel < ActiveRecord::Base
+      class FakeModel < ActiveRecord::Base
         establish_connection(
-          adapter:  "sqlite3",
-          database: "tmp/some"
+          adapter:  "fake"
         )
       end
       def test_type_can_be_used_with_various_db
@@ -19,8 +18,8 @@ def test_type_can_be_used_with_various_db
           ActiveRecord::Type.adapter_name_from(Account)
         )
         assert_equal(
-           :sqlite3,
-           ActiveRecord::Type.adapter_name_from(SqliteModel)
+           :fake,
+           ActiveRecord::Type.adapter_name_from(FakeModel)
         )
       end
     end

test/excludes/ActiveRecord/PostgresqlTransactionNestedTest.rb

@@ -1,2 +1,14 @@
-exclude :test_deadlock_raises_Deadlocked_inside_nested_SavepointTransaction, "Causes CI to hand. Skip while debugging."
-exclude :test_unserializable_transaction_raises_SerializationFailure_inside_nested_SavepointTransaction, "Causes CI to hand. Skip while debugging."
+
+# > In CRDB SERIALIZABLE, reads block on in-progress writes for
+# > as long as those writes are in progress. However, PG does
+# > not have this "read block on write" behavior, and so rather
+# > than allowing the left-hand-side to execute, it must instead
+# > abort that transaction. Both are valid ways to implement SERIALIZABLE.
+#
+# See discussion: https://github.com/cockroachdb/activerecord-cockroachdb-adapter/pull/333
+message = "SERIALIZABLE transactions are different in CockroachDB."
+
+exclude :test_deadlock_raises_Deadlocked_inside_nested_SavepointTransaction, message
+exclude :test_unserializable_transaction_raises_SerializationFailure_inside_nested_SavepointTransaction, message
+exclude :test_SerializationFailure_inside_nested_SavepointTransaction_is_recoverable, message
+exclude :test_deadlock_inside_nested_SavepointTransaction_is_recoverable, message

test/excludes/AttributeMethodsTest.rb

@@ -0,0 +1,2 @@
+# TODO: Rails 7.2 remove this exclusion
+exclude "test_#undefine_attribute_methods_undefines_alias_attribute_methods", "The test will be fixed in 7.2 (https://github.com/rails/rails/commit/a0993f81d0450a191da1ee35282f60fc2899135c)"