Bug#28718 Running backup testcase fails in mysql testsuite

 - Skip test if the mysqld to test is not started from MYSQLTEST_VARDIR

mysql-test/include/uses_vardir.inc

+#
+# Some tests uses LOAD DATA with a relative path
+# and need to see for example ../std_data
+#
+# Also if an absolute path was used, the server might be started
+# with --secure-file-priv and wouldn't be allowed to LOAD a file
+# outside of it's vardir anyway
+#
+
+let $datadir=
+  query_get_value("SHOW VARIABLES LIKE 'datadir'", Value, 1);
+if (`select LOCATE("$MYSQLTEST_VARDIR", "$datadir") != 1`)
+{
+  skip Need mysqld in MYSQLTEST_VARDIR;
+}

mysql-test/t/backup.test

+
+# The server need to be started in $MYSQLTEST_VARDIR since it
+# uses ../std_data_ln/
+-- source include/uses_vardir.inc
+
 #
 # This test is a bit tricky as we can't use backup table to overwrite an old
 # table

mysql-test/t/blackhole.test

@@ -5,6 +5,10 @@
 -- source include/not_embedded.inc
 -- source include/have_blackhole.inc
 
+# The server need to be started in $MYSQLTEST_VARDIR since it
+# uses ../std_data_ln/
+-- source include/uses_vardir.inc
+
 --disable_warnings
 drop table if exists t1,t2;
 --enable_warnings
@@ -109,7 +113,7 @@ insert into t1 values(1);
 insert ignore into t1 values(1);
 replace into t1 values(100);
 create table t2 (a varchar(200)) engine=blackhole;
-load data infile '../std_data_ln/words.dat' into table t2;
+eval load data infile '../std_data_ln/words.dat' into table t2;
 alter table t1 add b int;
 alter table t1 drop b;
 create table t3 like t1;