diff --git a/build.sh b/build.sh
index a36e4d4..824bee1 100755
--- a/build.sh
+++ b/build.sh
@@ -1,6 +1,7 @@
 #!/bin/bash
 #
-# This file is part of Builder.
+# Builder – Compile scripts for local installs of software packages.
+# Copyright (C) 2020 Forschungszentrum Jülich GmbH, INM-6
 #
 # Builder is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -15,6 +16,8 @@
 # You should have received a copy of the GNU General Public License
 # along with Builder.  If not, see <https://www.gnu.org/licenses/>.
 #
+# SPDX-License-Identifier: GPL-3.0-or-later
+#
 set -euo pipefail
 if [ -z "${BUILDER_PATH+x}" ]; then
 	BUILDER_PATH="$(dirname "$(realpath "$0")")"
diff --git a/build_functions.sh b/build_functions.sh
index 5842a68..8f10fb3 100644
--- a/build_functions.sh
+++ b/build_functions.sh
@@ -1,5 +1,7 @@
+#!/bin/bash
 #
-# This file is part of Builder.
+# Builder – Compile scripts for local installs of software packages.
+# Copyright (C) 2020 Forschungszentrum Jülich GmbH, INM-6
 #
 # Builder is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -14,6 +16,8 @@
 # You should have received a copy of the GNU General Public License
 # along with Builder.  If not, see <https://www.gnu.org/licenses/>.
 #
+# SPDX-License-Identifier: GPL-3.0-or-later
+#
 
 ################################################################################
 # Helper functions
diff --git a/tests/license-header.bats b/tests/license-header.bats
new file mode 100644
index 0000000..d7e70d5
--- /dev/null
+++ b/tests/license-header.bats
@@ -0,0 +1,72 @@
+#!/usr/bin/env bats
+load test_helper
+
+test_planfiles_startwith() {
+	# This helper function searches for all files matching $2 pattern
+	# and complains about those not matching $1 regex.
+	FILESTART="$1"
+	NLINES="$(echo "$FILESTART" | wc -l)"
+	N_BAD=0
+	for file in $(find "$BATS_TEST_DIRNAME/../plans" -type f -not -name "*.module" -not -name "*.txt" -not -name "*.sw*"); do
+		[ "$FILESTART" = "$(head -n $NLINES "$file")" ] || {
+			echo "$file does not contain correct copyright statement";
+			echo ""
+			head -n $NLINES "$file" | diff -u /dev/stdin --label "$file" /dev/fd/9 --label "correct" 9<<<"$FILESTART"
+			echo ""
+			N_BAD=$(( $N_BAD + 1 ))
+		};
+	done
+	[ $N_BAD -eq 0 ] || {
+		echo "$N_BAD BAD FILES"
+		false
+	}
+}
+
+test_codefiles_startwith() {
+	# This helper function searches for all files matching $2 pattern
+	# and complains about those not matching $1 regex.
+	FILESTART="$1"
+	NLINES="$(echo "$FILESTART" | wc -l)"
+	N_BAD=0
+	for file in $(find "$BATS_TEST_DIRNAME/.." -maxdepth 2 -type f -name "*.sh"); do
+		[ "$FILESTART" = "$(head -n $NLINES "$file")" ] || {
+			echo "$file does not contain correct copyright statement";
+			echo ""
+			head -n $NLINES "$file" | diff -u /dev/stdin --label "$file" /dev/fd/9 --label "correct" 9<<<"$FILESTART"
+			echo ""
+			N_BAD=$(( $N_BAD + 1 ))
+		};
+	done
+	[ $N_BAD -eq 0 ] || {
+		echo "$N_BAD BAD FILES"
+		false
+	}
+}
+
+@test "check planfiles start with LICENSE header" {
+	run test_planfiles_startwith "$(<$BATS_TEST_DIRNAME/license-header.txt)"
+	if [ ${status} -ne 0 ]; then
+		cat <<EOT
+---------------------------------------------------------------------------
+Planfiles that are part of builder should start with an appropriate copyright
+header. Please open any planfile and copy the first 16 lines verbatim into any
+new planfile.
+---------------------------------------------------------------------------
+EOT
+		emit_debug_output && return 1
+	fi
+}
+
+@test "check source code starts with LICENSE header" {
+	run test_codefiles_startwith "$(<$BATS_TEST_DIRNAME/license-header.txt)"
+	if [ ${status} -ne 0 ]; then
+		cat <<EOT
+---------------------------------------------------------------------------
+Source code that are part of builder should start with an appropriate copyright
+header. Please make sure each file starts exactly (!) with the content of the
+file "tests/license-header.txt"
+---------------------------------------------------------------------------
+EOT
+		emit_debug_output && return 1
+	fi
+}
diff --git a/tests/license-header.txt b/tests/license-header.txt
new file mode 100644
index 0000000..b00cd4a
--- /dev/null
+++ b/tests/license-header.txt
@@ -0,0 +1,20 @@
+#!/bin/bash
+#
+# Builder – Compile scripts for local installs of software packages.
+# Copyright (C) 2020 Forschungszentrum Jülich GmbH, INM-6
+#
+# Builder is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Builder is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Builder.  If not, see <https://www.gnu.org/licenses/>.
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+#
diff --git a/tests/planfiles.bats b/tests/planfiles.bats
index e9db043..990fda7 100644
--- a/tests/planfiles.bats
+++ b/tests/planfiles.bats
@@ -19,27 +19,6 @@ test_files_contain() {
 	}
 }
 
-test_planfiles_startwith() {
-	# This helper function seaches for all files matching $2 pattern
-	# and complains about those not matching $1 regex.
-	FILESTART="$1"
-	NLINES="$(echo "$FILESTART" | wc -l)"
-	N_BAD=0
-	for file in $(find "$BATS_TEST_DIRNAME/../plans" -type f -not -name "*.module" -not -name "*.txt" -not -name "*.sw*"); do
-		[ "$FILESTART" = "$(head -n $NLINES "$file")" ] || {
-			echo "$file does not contain correct copyright statement";
-			echo ""
-			head -n $NLINES "$file" | diff -u /dev/stdin --label "$file" /dev/fd/9 --label "correct" 9<<<"$FILESTART"
-			echo ""
-			N_BAD=$(( $N_BAD + 1 ))
-		};
-	done
-	[ $N_BAD -eq 0 ] || {
-		echo "$N_BAD BAD FILES"
-		false
-	}
-}
-
 @test "modules contain 'PREREQ_DEPENDS'" {
 	run test_files_contain 'PREREQ_DEPENDS' "*.module"
 	if [ ${status} -ne 0 ]; then
@@ -110,38 +89,3 @@ EOT
 		emit_debug_output && return 1
 	fi
 }
-
-@test "check planfiles start with LICENSE header" {
-	FILESTART="#!/bin/bash
-#
-# Builder – Compile scripts for local installs of software packages.
-# Copyright (C) 2020 Forschungszentrum Jülich GmbH, INM-6
-#
-# Builder is free software: you can redistribute it and/or modify
-# it under the terms of the GNU General Public License as published by
-# the Free Software Foundation, either version 3 of the License, or
-# (at your option) any later version.
-#
-# Builder is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-# GNU General Public License for more details.
-#
-# You should have received a copy of the GNU General Public License
-# along with Builder.  If not, see <https://www.gnu.org/licenses/>.
-#
-# SPDX-License-Identifier: GPL-3.0-or-later
-#"
-
-	run test_planfiles_startwith "$FILESTART"
-	if [ ${status} -ne 0 ]; then
-		cat <<EOT
----------------------------------------------------------------------------
-Planfiles that are part of builder should start with an appropriate copyright
-header. Please open any planfile and copy the first 16 lines verbatim into any
-new planfile.
----------------------------------------------------------------------------
-EOT
-		emit_debug_output && return 1
-	fi
-}