Another try :)

[...]

    Support for platform-specific test configuration
     - Platform-specific functionality is stored in test-config-PLATFORM.sh files
     - configure script creates a test/test-config.sh depending on the platform
     - test-lib.sh loads test-config.sh file
     - Some platform-specific functionality included for gnu/bsd:
       - Work-around for touch -d on BSD
       - Variable to store sed command for extended expressions

diff --git a/configure b/configure
index bbf30cd..053a4a1 100755
--- a/configure
+++ b/configure
@@ -16,6 +16,13 @@ if [ "$srcdir" != "." ]; then
     # whole thing into the build directory.
     cp -a "$srcdir"/test/* test
 
+    # Platform specific test configuration
+    if [ $platform = MACOSX ] ; then
+	cp test/test-config-bsd.sh test/test-config.sh
+    else
+	cp test/test-config-gnu.sh test/test-config.sh
+    fi
+
     # Emacs only likes to generate compiled files next to the .el files
     # by default so copy these as well (which is not ideal0.
     cp -a "$srcdir"/emacs/*.el emacs
diff --git a/test/basic b/test/basic
index 808c968..5fbedfe 100755
--- a/test/basic
+++ b/test/basic
@@ -54,13 +54,14 @@ test_begin_subtest 'Ensure that all available tests will be run by notmuch-test'
 eval $(sed -n -e '/^TESTS="$/,/^"$/p' notmuch-test ../notmuch-test)
 tests_in_suite=$(for i in $TESTS; do echo $i; done | sort)
 available=$(ls -1 ../ | \
-    sed -r -e "/^(aggregate-results.sh|Makefile|Makefile.local|notmuch-test)/d" \
-	   -e "/^(README|test-lib.sh|test-lib.el|test-results|tmp.*|valgrind|corpus*)/d" \
-	   -e "/^(emacs.expected-output|smtp-dummy|smtp-dummy.c|test-verbose)/d" \
-	   -e "/^(test.expected-output|.*~)/d" \
-	   -e "/^(gnupg-secret-key.asc)/d" \
-	   -e "/^(gnupg-secret-key.NOTE)/d" \
-	   | sort)
+    $SED_EXTENDED -e "/^(aggregate-results.sh|Makefile|Makefile.local|notmuch-test)/d" \
+    		  -e "/^(README|test-lib.sh|test-lib.el|test-results|tmp.*|valgrind|corpus*)/d" \
+    		  -e "/^(emacs.expected-output|smtp-dummy|smtp-dummy.c|test-verbose)/d" \
+	   	  -e "/^(test.expected-output|.*~)/d" \
+	   	  -e "/^(gnupg-secret-key.asc)/d" \
+	   	  -e "/^(gnupg-secret-key.NOTE)/d" \
+	   	  -e "/^(test-config*)/d" \
+	   	  | sort)
 test_expect_equal "$tests_in_suite" "$available"
 
 EXPECTED=../test.expected-output
diff --git a/test/test-config-bsd.sh b/test/test-config-bsd.sh
new file mode 100644
index 0000000..e35d2fa
--- /dev/null
+++ b/test/test-config-bsd.sh
@@ -0,0 +1,23 @@
+# This file contains helper functions and other values that are
+# require platform-specific functionality (e.g., differing between GNU
+# and BSD). The configure script is used to identify the appropriate
+# file for a given platform, and copies the file test-config-FOO.sh to
+# test-config.sh, where FOO is the respective platform (bsd or gnu).
+#
+# This file is BSD-specific.
+
+# Syntax for extended expressions
+SED_EXTENDED="sed -E"
+
+# There is no touch -d on BSD, therefore we have to use a more tedious
+# version that uses date/stat to increment a date by a single second.
+increment_mtime_amount=0
+increment_mtime ()
+{
+    dir="$1"
+    
+    last_mod_date=`date -j -f %Y%m%d%H%M%S \`stat -f %Sm -t %Y%m%d%H%M%S ${dir}\` +%s`
+    increment_mtime_amount=$((increment_mtime_amount + 1))
+    new_date=`date -j -r ${last_mod_date} -v+${increment_mtime_amount}S +%Y%m%d%H%M.%S`
+    touch -t ${new_date} ${dir}
+}
diff --git a/test/test-config-gnu.sh b/test/test-config-gnu.sh
new file mode 100644
index 0000000..596505a
--- /dev/null
+++ b/test/test-config-gnu.sh
@@ -0,0 +1,20 @@
+# This file contains helper functions and other values that are
+# require platform-specific functionality (e.g., differing between GNU
+# and BSD). The configure script is used to identify the appropriate
+# file for a given platform, and copies the file test-config-FOO.sh to
+# test-config.sh, where FOO is the respective platform (bsd or gnu).
+#
+# This file is GNU-specific.
+
+# Syntax for extended expressions
+SED_EXTENDED="sed -r"
+
+# Use touch to increment the modification date by a single second.
+increment_mtime_amount=0
+increment_mtime ()
+{
+    dir="$1"
+
+    increment_mtime_amount=$((increment_mtime_amount + 1))
+    touch -d "+${increment_mtime_amount} seconds" "$dir"
+}
diff --git a/test/test-lib.sh b/test/test-lib.sh
index 922b1ef..1aa3a1c 100755
--- a/test/test-lib.sh
+++ b/test/test-lib.sh
@@ -23,6 +23,9 @@ if [ ${BASH_VERSINFO[0]} -lt 4 ]; then
     exit 1
 fi
 
+# Load platform-specific values
+. ./test-config.sh
+
 # if --tee was passed, write the output not only to the terminal, but
 # additionally to the file test-results/$BASENAME.out, too.
 case "$GIT_TEST_TEE_STARTED, $* " in
@@ -214,14 +217,6 @@ remove_cr () {
 }
 
 # Notmuch helper functions
-increment_mtime_amount=0
-increment_mtime ()
-{
-    dir="$1"
-
-    increment_mtime_amount=$((increment_mtime_amount + 1))
-    touch -d "+${increment_mtime_amount} seconds" "$dir"
-}
 
 # Generate a new message in the mail directory, with a unique message
 # ID and subject. The message is not added to the index.
@@ -514,7 +509,7 @@ NOTMUCH_NEW ()
 
 notmuch_search_sanitize ()
 {
-    sed -r -e 's/("?thread"?: ?)("?)................("?)/\1\2XXX\3/'
+    $SED_EXTENDED 's/("?thread"?: ?)("?)................("?)/\1\2XXX\3/'
 }
 
 NOTMUCH_SHOW_FILENAME_SQUELCH='s,filename:.*/mail,filename:/XXX/mail,'