prefer drop_table if_exists: true over raw SQL.

/cc @yahonda

This makes it easier for third party adapters to run our tests,
even if that database does not support IF EXISTS.

activerecord/test/cases/adapters/mysql/mysql_adapter_test.rb

@@ -15,7 +15,7 @@ module ActiveRecord
         assert_raise ActiveRecord::NoDatabaseError do
           configuration = ActiveRecord::Base.configurations['arunit'].merge(database: 'inexistent_activerecord_unittest')
           connection = ActiveRecord::Base.mysql_connection(configuration)
-          connection.exec_query('drop table if exists ex')
+          connection.drop_table 'ex', if_exists: true
         end
       end
 

activerecord/test/cases/adapters/mysql/schema_test.rb

@@ -22,7 +22,7 @@ module ActiveRecord
       end
 
       teardown do
-        @connection.execute "drop table if exists mysql_doubles"
+        @connection.drop_table "mysql_doubles", if_exists: true
       end
 
       class MysqlDouble < ActiveRecord::Base

activerecord/test/cases/adapters/mysql2/connection_test.rb

@@ -22,7 +22,7 @@ class MysqlConnectionTest < ActiveRecord::TestCase
     assert_raise ActiveRecord::NoDatabaseError do
       configuration = ActiveRecord::Base.configurations['arunit'].merge(database: 'inexistent_activerecord_unittest')
       connection = ActiveRecord::Base.mysql2_connection(configuration)
-      connection.exec_query('drop table if exists ex')
+      connection.drop_table 'ex', if_exists: true
     end
   end
 

activerecord/test/cases/adapters/postgresql/array_test.rb

@@ -28,7 +28,7 @@ class PostgresqlArrayTest < ActiveRecord::TestCase
   end
 
   teardown do
-    @connection.execute 'drop table if exists pg_arrays'
+    @connection.drop_table 'pg_arrays', if_exists: true
     disable_extension!('hstore', @connection)
   end
 

activerecord/test/cases/adapters/postgresql/bytea_test.rb

@@ -20,7 +20,7 @@ class PostgresqlByteaTest < ActiveRecord::TestCase
   end
 
   teardown do
-    @connection.execute 'drop table if exists bytea_data_type'
+    @connection.drop_table 'bytea_data_type', if_exists: true
   end
 
   def test_column

activerecord/test/cases/adapters/postgresql/hstore_test.rb

@@ -32,7 +32,7 @@ if ActiveRecord::Base.connection.supports_extensions?
     end
 
     teardown do
-      @connection.execute 'drop table if exists hstores'
+      @connection.drop_table 'hstores', if_exists: true
     end
 
     def test_hstore_included_in_extensions

activerecord/test/cases/adapters/postgresql/integer_test.rb

@@ -16,7 +16,7 @@ class PostgresqlIntegerTest < ActiveRecord::TestCase
   end
 
   teardown do
-    @connection.execute "drop table if exists pg_integers"
+    @connection.drop_table "pg_integers", if_exists: true
   end
 
   test "schema properly respects bigint ranges" do

activerecord/test/cases/adapters/postgresql/ltree_test.rb

@@ -22,7 +22,7 @@ class PostgresqlLtreeTest < ActiveRecord::TestCase
   end
 
   teardown do
-    @connection.execute 'drop table if exists ltrees'
+    @connection.drop_table 'ltrees', if_exists: true
   end
 
   def test_column

activerecord/test/cases/adapters/postgresql/uuid_test.rb

@@ -7,7 +7,7 @@ module PostgresqlUUIDHelper
   end
 
   def drop_table(name)
-    connection.execute "drop table if exists #{name}"
+    connection.drop_table name, if_exists: true
   end
 end
 

activerecord/test/cases/adapters/postgresql/xml_test.rb

@@ -22,7 +22,7 @@ class PostgresqlXMLTest < ActiveRecord::TestCase
   end
 
   teardown do
-    @connection.execute 'drop table if exists xml_data_type'
+    @connection.drop_table 'xml_data_type', if_exists: true
   end
 
   def test_column

activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb

@@ -22,7 +22,7 @@ module ActiveRecord
       def test_bad_connection
         assert_raise ActiveRecord::NoDatabaseError do
           connection = ActiveRecord::Base.sqlite3_connection(adapter: "sqlite3", database: "/tmp/should/_not/_exist/-cinco-dog.db")
-          connection.exec_query('drop table if exists ex')
+          connection.drop_table 'ex', if_exists: true
         end
       end
 

activerecord/test/cases/transactions_test.rb

@@ -668,7 +668,7 @@ class TransactionTest < ActiveRecord::TestCase
       end
     end
   ensure
-    connection.execute("DROP TABLE IF EXISTS transaction_without_primary_keys")
+    connection.drop_table 'transaction_without_primary_keys', if_exists: true
   end
 
   private