Fix grammar error in testing.adoc

- Fixes grammatical error in the Unit Testing section

Signed-off-by: Anil Kutahyali <anilkutahyali@gmail.com>
(cherry picked from commit de88c8c)

Author: nakutahyali

spring-batch-docs/modules/ROOT/pages/testing.adoc

@@ -4,7 +4,7 @@
 
 As with other application styles, it is extremely important to unit test any code written
 as part of a batch job. The Spring core documentation covers how to unit and integration
-test with Spring in great detail, so it is not be repeated here. It is important, however,
+test with Spring in great detail, so it will not be repeated here. It is important, however,
 to think about how to "`end to end`" test a batch job, which is what this chapter covers.
 The `spring-batch-test` project includes classes that facilitate this end-to-end test
 approach.