test: add a script to figure out source and build directories

Expect the tests to be run somewhere in the build directory
hierarchy. Allow for source and build directories to be passed through
the environment.

test/export-dirs.sh

@@ -0,0 +1,32 @@
+# Source this script to set and export NOTMUCH_SRCDIR and
+# NOTMUCH_BUILDDIR.
+#
+# For this to work, always have current directory somewhere within the
+# build directory hierarchy, and run the script sourcing this script
+# using a path (relative or absolute) to the source directory.
+
+if [[ -z "${NOTMUCH_SRCDIR}" ]]; then
+	export NOTMUCH_SRCDIR="$(cd "$(dirname "$0")"/.. && pwd)"
+fi
+
+find_builddir()
+{
+	local dir="$1"
+
+	while [[ -n "$dir" ]] && [[ "$dir" != "/" ]]; do
+		if [[ -x "$dir/notmuch" ]] && [[ ! -d "$dir/notmuch" ]]; then
+			echo "$dir"
+			break
+		fi
+		dir="$(dirname "$dir")"
+	done
+}
+
+if [[ -z "${NOTMUCH_BUILDDIR}" ]]; then
+	export NOTMUCH_BUILDDIR="$(find_builddir "$(pwd)")"
+
+	if [[ -z "${NOTMUCH_BUILDDIR}" ]]; then
+		echo "Run tests in a subdir of built notmuch tree." >&2
+		exit 1
+	fi
+fi