Small tests for unsafe msg request (#912)

* Small tests for unsafe msg request

* Remove bad eltype test

Author: kshyatt

test/test_test.jl

@@ -70,6 +70,10 @@ resize!(reqs, 4)
 @test length(reqs) == 4
 @test all(MPI.isnull, reqs)
 
+resize!(reqs, 2)
+@test length(reqs) == 2
+@test all(MPI.isnull, reqs)
+
 reqs = MPI.UnsafeMultiRequest(2)
 GC.@preserve send_mesg recv_mesg begin
     MPI.Irecv!(recv_mesg, comm, reqs[1]; source=src, tag=src+32)
@@ -87,5 +91,9 @@ resize!(reqs, 4)
 @test length(reqs) == 4
 @test all(MPI.isnull, reqs)
 
+resize!(reqs, 2)
+@test length(reqs) == 2
+@test all(MPI.isnull, reqs)
+
 MPI.Finalize()
 @test MPI.Finalized()