diff --git a/tools/csv-concat-test.sh b/tools/csv-concat-test.sh
@@ -0,0 +1,34 @@
+#!/bin/bash
+#
+# Usage:
+#   ./csv-concat-test.sh <function name>
+
+set -o nounset
+set -o pipefail
+set -o errexit
+
+test-good() {
+  mkdir -p _tmp
+  cat >_tmp/test1.csv <<EOF
+name,age
+alice,0
+bob,10
+EOF
+
+  cat >_tmp/test2.csv <<EOF
+name,age
+carol,20
+EOF
+
+  ./csv_concat.py _tmp/test{1,2}.csv
+
+  cat >_tmp/bad.csv <<EOF
+name,age,another
+dave,30,oops
+EOF
+
+  ./csv_concat.py _tmp/test{1,2}.csv _tmp/bad.csv
+
+}
+
+"$@"
diff --git a/tools/csv_concat.py b/tools/csv_concat.py
@@ -0,0 +1,35 @@
+#!/usr/bin/python
+"""
+csv_concat.py
+"""
+
+import sys
+
+
+def main(argv):
+  first_header = None
+  for path in argv[1:]:
+    with open(path) as f:
+      # Assume
+      header = f.readline()
+      if first_header is None:
+        sys.stdout.write(header)
+        first_header = header.strip()
+      else:
+        h = header.strip()
+        if h != first_header:
+          raise RuntimeError(
+              'Invalid header in %r: %r.  Expected %r' % (path, h,
+              first_header))
+      # Now print rest of lines
+      for line in f:
+        sys.stdout.write(line)
+
+
+
+if __name__ == '__main__':
+  try:
+    main(sys.argv)
+  except RuntimeError as e:
+    print >>sys.stderr, 'FATAL: %s' % e
+    sys.exit(1)