Merge pull request rails#6616 from dpassage/fix_resolver_test_sqlite3

Resolver tests fail if mysql adapter not installed

Author: carlosantoniodasilva

activerecord/test/cases/connection_specification/resolver_test.rb

@@ -9,6 +9,7 @@ def resolve(spec)
         end
 
         def test_url_host_no_db
+          skip "only if mysql is available" unless defined?(MysqlAdapter)
           spec = resolve 'mysql://foo?encoding=utf8'
           assert_equal({
             :adapter  => "mysql",
@@ -18,6 +19,7 @@ def test_url_host_no_db
         end
 
         def test_url_host_db
+          skip "only if mysql is available" unless defined?(MysqlAdapter)
           spec = resolve 'mysql://foo/bar?encoding=utf8'
           assert_equal({
             :adapter  => "mysql",
@@ -27,6 +29,7 @@ def test_url_host_db
         end
 
         def test_url_port
+          skip "only if mysql is available" unless defined?(MysqlAdapter)
           spec = resolve 'mysql://foo:123?encoding=utf8'
           assert_equal({
             :adapter  => "mysql",