testsuite: Introduce gdb_assert

Often we'll do something like:

    if {$ok} {
	fail "whatever"
    } else {
	pass "whatever"
    }

This adds a helper procedure for that, and converts one random place
to use it, as an example.

2014-07-14  Pedro Alves  <palves@redhat.com>

	* lib/gdb.exp (gdb_assert): New procedure.
	* gdb.trace/backtrace.exp (gdb_backtrace_tdp_4): Use it.

1 files changed, 2 insertions, 5 deletions

diff --git a/gdb/testsuite/gdb.trace/backtrace.exp b/gdb/testsuite/gdb.trace/backtrace.exp
index a74fc3f..cb50f06 100644
--- a/gdb/testsuite/gdb.trace/backtrace.exp
+++ b/gdb/testsuite/gdb.trace/backtrace.exp
@@ -256,11 +256,8 @@ proc gdb_backtrace_tdp_4 { msg depth traceframe } {
 
 	# Output of 'tdump' on frame 0 and frame 1 should be
 	# identical.
-	if ![string compare $output_string0 $output_string1]  {
-	    pass "tdump output"
-	} else {
-	    fail "tdump output"
-	}
+	gdb_assert ![string compare $output_string0 $output_string1] \
+	    "tdump output"
     }
 }