[gdb/testsuite] Restore breakpoint command in ui-redirect.exp

In gdb.base/ui-redirect.exp, the "save breakpoint" command is used to write
the current breakpoints to a file, but the actual output is not verified.

Consequently, the test has regressed in that the "print 1" command associated
with a breakpoint on main is removed by a subsequent runto_main, which first
deletes all breakpoints:
...
(gdb) break main
Breakpoint 1 at 0x4004d7: file start.c, line 34.
(gdb) commands
Type commands for breakpoint(s) 1, one per line.
End with a line saying just "end".
> PASS: gdb.base/ui-redirect.exp: commands
print 1
> PASS: gdb.base/ui-redirect.exp: print 1
end
(gdb) PASS: gdb.base/ui-redirect.exp: end
delete breakpoints
Delete all breakpoints? (y or n) y
...
and consequently the "save breakpoint" output is missing the breakpoint
command for main:
...
 break main
-  commands
-    print 1
-  end
 break foo
 break bar
...

Fix this by replacing "gdb_breakpoint main" with runto_main, and verifying the
"save breakpoints" output.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2019-09-05  Tom de Vries  <tdevries@suse.de>

	* lib/gdb.exp (cmp_file_string): New proc.
	* gdb.base/ui-redirect.exp: Replace "gdb_breakpoint main" with
	runto_main.  Verify save breakpoints output.

---
 gdb/testsuite/gdb.base/ui-redirect.exp | 33 +++++++++++++++++++++++++--------
 gdb/testsuite/lib/gdb.exp              | 27 +++++++++++++++++++++++++++
 2 files changed, 52 insertions(+), 8 deletions(-)

diff --git a/gdb/testsuite/gdb.base/ui-redirect.exp b/gdb/testsuite/gdb.base/ui-redirect.exp
index 4507ac51a2..3da30cd7f7 100644
--- a/gdb/testsuite/gdb.base/ui-redirect.exp
+++ b/gdb/testsuite/gdb.base/ui-redirect.exp
@@ -23,7 +23,10 @@ if { [prepare_for_testing "failed to prepare" ui-redirect start.c] } {
     return -1
 }
 
-gdb_breakpoint main
+if ![runto_main] {
+    fail "can't run to main"
+    return -1
+}
 
 set test "commands"
 gdb_test_multiple $test $test {
@@ -40,18 +43,29 @@ gdb_test_multiple $test $test {
 }
 gdb_test_no_output "end"
 
-if ![runto_main] {
-    fail "can't run to main"
-    return -1
-}
 gdb_breakpoint "foo"
 gdb_breakpoint "bar"
 
+set cmds \
+    [list \
+	 "break main" \
+	 "  commands" \
+	 "    print 1" \
+	 "  end" \
+	 "break foo" \
+	 "break bar"]
+set cmds [join $cmds "\n"]
+set cmds "$cmds\n"
+set outdir [standard_output_file {}]
+set cmds_file "$outdir/cmds.txt"
+
 with_test_prefix "logging" {
     gdb_test_no_output "set logging file /dev/null"
     gdb_test "set logging on" \
     "Copying output to /dev/null.*Copying debug output to /dev/null\\."
-    gdb_test "save breakpoints /dev/null" "Saved to file '/dev/null'\\."
+    gdb_test "save breakpoints $cmds_file" "Saved to file '$cmds_file'\\." \
+	"save breakpoints cmds.txt"
+    cmp_file_string "$cmds_file" "$cmds" "cmds.txt"
     gdb_test "set logging off" "Done logging to /dev/null\\."
     gdb_test "help" "List of classes of commands:.*"
 }
@@ -60,7 +74,8 @@ with_test_prefix "redirect" {
     gdb_test "set logging redirect on"
     gdb_test "set logging on" \
     "Redirecting output to /dev/null.*Copying debug output to /dev/null\\."
-    gdb_test_no_output "save breakpoints /dev/null"
+    gdb_test_no_output "save breakpoints $cmds_file" "save breakpoints cmds.txt"
+    cmp_file_string "$cmds_file" "$cmds" "cmds.txt"
     gdb_test "set logging off" "Done logging to /dev/null\\."
     gdb_test "help" "List of classes of commands:.*"
 }
@@ -71,7 +86,9 @@ with_test_prefix "redirect while already logging" {
     "Copying output to /dev/null.*Copying debug output to /dev/null\\."
     gdb_test "set logging redirect on" \
     ".*warning: Currently logging .*Turn the logging off and on to make the new setting effective.*"
-    gdb_test "save breakpoints /dev/null" "Saved to file '/dev/null'\\."
+    gdb_test "save breakpoints $cmds_file" "Saved to file '$cmds_file'\\." \
+	"save breakpoints cmds.txt"
+    cmp_file_string "$cmds_file" "$cmds" "cmds.txt"
     gdb_test "set logging off" "Done logging to /dev/null\\."
     gdb_test "help" "List of classes of commands:.*"
     gdb_test_no_output "set logging redirect off"
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index 76805fb5ec..6ceec00e37 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -6668,5 +6668,32 @@ proc gdb_write_cmd_file { cmdline } {
     catch "close $cmd_file"
 }
 
+# Compare contents of FILE to string STR. Pass with MSG if equal, otherwise
+# fail with MSG.
+
+proc cmp_file_string { file str msg } {
+    if { ![file exists $file]} {
+	fail "$msg"
+	return
+    }
+
+    set caught_error [catch {
+	set fp [open "$file" r]
+	set file_contents [read $fp]
+	close $fp
+    } error_message]
+    if { $caught_error } then {
+	error "$error_message"
+	fail "$msg"
+	return
+    }
+
+    if { $file_contents == $str } {
+	pass "$msg"
+    } else {
+	fail "$msg"
+    }
+}
+
 # Always load compatibility stuff.
 load_lib future.exp