diff --git a/tests/auth/writeoldkey-t b/tests/auth/writeoldkey-t
index 3240212942..614dcb6031 100755
--- a/tests/auth/writeoldkey-t
+++ b/tests/auth/writeoldkey-t
@@ -2,9 +2,11 @@
 
 use strict;
 use warnings;
+use lib $ENV{C_TAP_SOURCE} . "/tests-lib/perl5";
+
+use afstest qw(src_path obj_path);
 use Test::More;
 use File::Temp qw/tempdir/;
-use FindBin qw($Bin);
 use Cwd qw/abs_path/;
 use File::Compare;
 use Sys::Hostname;
@@ -19,20 +21,10 @@ if (!defined(gethostbyname(hostname()))) {
 }
 plan tests => 1;
 
-my $cmd;
-if (defined($ENV{C_TAP_BUILD})) {
-    $cmd = $ENV{C_TAP_BUILD} . "/auth/writekeyfile";
-} else {
-    $cmd = $Bin . "/writekeyfile";
-}
+my $cmd = obj_path("tests/auth/writekeyfile");
 $cmd = abs_path($cmd);
 
-my $keyfile;
-if (defined($ENV{C_TAP_SOURCE})) {
-    $keyfile = $ENV{C_TAP_SOURCE} . "/auth/KeyFile.short";
-} else {
-    $keyfile = $Bin . "/KeyFile.short";
-}
+my $keyfile = src_path("tests/auth/KeyFile.short");
 $keyfile = abs_path($keyfile);
 
 my $dir = tempdir('afs_XXXXXX', CLEANUP => 1);
diff --git a/tests/opr/softsig-t b/tests/opr/softsig-t
index d750d98dde..66a2648278 100755
--- a/tests/opr/softsig-t
+++ b/tests/opr/softsig-t
@@ -24,6 +24,9 @@
 
 use strict;
 use warnings;
+use lib $ENV{C_TAP_SOURCE} . "/tests-lib/perl5";
+
+use afstest qw(obj_path);
 use Test::More tests => 11;
 use IO::File;
 use POSIX qw(:signal_h);
@@ -33,16 +36,7 @@ use FindBin qw($Bin);
 # Start up our test process, and send it various signals. Check that these
 # signals make it to it correctly, and are reported on the command line.
 
-my $softsig_helper;
-
-# Our softsig helper should be in $TOP_OBJDIR/tests/opr. To calculate that
-# path, use the C_TAP_BUILD env var if the test harness has set it; otherwise,
-# our next best guess is that it's in the same dir as this script.
-if (defined($ENV{C_TAP_BUILD})) {
-    $softsig_helper = $ENV{C_TAP_BUILD} . "/opr/softsig-helper";
-} else {
-    $softsig_helper = $Bin . "/softsig-helper";
-}
+my $softsig_helper = obj_path("tests/opr/softsig-helper");
 
 # This -dummy argument prevents Perl from putting an intermediate sh
 # -c between us and softsig-helper in the case where the build
diff --git a/tests/ptserver/pt_util-t b/tests/ptserver/pt_util-t
index 0f5c84ae0c..af97668922 100755
--- a/tests/ptserver/pt_util-t
+++ b/tests/ptserver/pt_util-t
@@ -2,17 +2,14 @@
 
 use strict;
 use warnings;
+use lib $ENV{C_TAP_SOURCE} . "/tests-lib/perl5";
 
+use afstest qw(obj_path);
 use File::Basename;
 use File::Temp qw(tempfile);
 use Test::More tests=>2;
 
-my $builddir = $ENV{C_TAP_BUILD};
-if (!$builddir) {
-  $builddir = dirname($0)."/..";
-}
-
-$builddir.="/..";
+my $pt_util = obj_path("src/ptserver/pt_util");
 
 (undef, my $prdbfile) = tempfile("prdbtest.XXXXXX", TMPDIR => 1, UNLINK => 1);
 
@@ -35,13 +32,13 @@ EOF
 
 my $fh;
 
-open $fh, '|-', "$builddir/src/ptserver/pt_util", '-w', '-p', $prdbfile
+open $fh, '|-', "$pt_util", '-w', '-p', $prdbfile
    or die "Failed to start pt_util for DB creation\n";
 print $fh $instructions;
 close($fh)
    or die "pt util failed while creating DB\n";
 
-open $fh, '-|', "$builddir/src/ptserver/pt_util", '-p', $prdbfile,
+open $fh, '-|', "$pt_util", '-p', $prdbfile,
 				     '-user', '-group', '-members'
     or die "Failed to start pt_util for DB reading\n";
 
diff --git a/tests/rx/perf-t b/tests/rx/perf-t
index 406c31f828..0fc2cadf68 100755
--- a/tests/rx/perf-t
+++ b/tests/rx/perf-t
@@ -2,14 +2,14 @@
 
 use strict;
 use warnings;
+use lib $ENV{C_TAP_SOURCE} . "/tests-lib/perl5";
 
+use afstest qw(obj_path);
 use Test::More tests=>4;
 use POSIX qw(:sys_wait_h :signal_h);
 
 my $port = 4000;
-my $build = $ENV{C_TAP_BUILD};
-$build = ".." if (!defined($build));
-my $rxperf = $build."/../src/tools/rxperf/rxperf";
+my $rxperf = obj_path("src/tools/rxperf/rxperf");
 
 # Start up an rxperf server
 
diff --git a/tests/tests-lib/perl5/afstest.pm b/tests/tests-lib/perl5/afstest.pm
new file mode 100644
index 0000000000..b2ee9bcdf6
--- /dev/null
+++ b/tests/tests-lib/perl5/afstest.pm
@@ -0,0 +1,61 @@
+# Copyright (c) 2020 Sine Nomine Associates. All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE AUTHOR `AS IS'' AND ANY EXPRESS OR
+# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+# OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+# IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+# NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+# THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package afstest;
+require Exporter;
+our @ISA = qw(Exporter);
+our @EXPORT_OK = qw(src_path obj_path);
+
+sub
+x_path($;$)
+{
+    my ($env_var, $path) = @_;
+    my $tdir = $ENV{$env_var};
+    if (!defined($tdir)) {
+	# If C_TAP_SOURCE/C_TAP_BUILD isn't set, we assume we're running from
+	# the same cwd as one of the test programs (e.g. 'tests/foo/'). So to
+	# get to 'tests/', just go up one level.
+	$tdir = "..";
+    }
+
+    # $tdir now represents the 'tests/' dir. Go one level up to get to the
+    # top-level dir.
+    if (defined($path)) {
+	return "$tdir/../$path";
+    } else {
+	return "$tdir/..";
+    }
+}
+
+sub
+src_path(;$)
+{
+    my $path = $_[0];
+    return x_path("C_TAP_SOURCE", $path);
+}
+
+sub
+obj_path(;$)
+{
+    my $path = $_[0];
+    return x_path("C_TAP_BUILD", $path);
+}
diff --git a/tests/tests-lib/perl5/mancheck_utils.pm b/tests/tests-lib/perl5/mancheck_utils.pm
index 62e1693cf6..540c1fc1ec 100644
--- a/tests/tests-lib/perl5/mancheck_utils.pm
+++ b/tests/tests-lib/perl5/mancheck_utils.pm
@@ -11,6 +11,7 @@
 #
 use File::Basename;
 use Test::More;
+use afstest qw(src_path obj_path);
 
 sub check_command_binary {
     my $c = shift(@_);
@@ -99,12 +100,8 @@ sub test_command_man_pages {
 sub run_manpage_tests($$) {
     my ($subdir, $command) = @_;
 
-    # When run from 'runtests', our cwd will be TOP_OBJDIR/tests. $C_TAP_SOURCE
-    # is set to TOP_SRCDIR/tests, and $C_TAP_BUILD is set to TOP_OBJDIR/tests.
-    # We want the top-level src and obj dirs, in order to find the relevant
-    # binaries and manpages.
-    my $srcdir = $ENV{C_TAP_SOURCE} . "/..";
-    my $objdir = $ENV{C_TAP_BUILD} . "/..";
+    my $srcdir = src_path();
+    my $objdir = obj_path();
 
     my @sub_commands = lookup_sub_commands("$objdir/$subdir", $command);
     die("No subcommands found in $objdir/$subdir/$command?") unless(@sub_commands);