sgrep: add smoke test

pkgs/tools/text/sgrep/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, lib, m4, makeWrapper }:
+{ stdenv, sgrep, fetchurl, runCommand, lib, m4, makeWrapper }:
 
 stdenv.mkDerivation rec {
   pname = "sgrep";
@@ -16,6 +16,14 @@ stdenv.mkDerivation rec {
       --prefix PATH : ${lib.makeBinPath [ m4 ]}
   '';
 
+  passthru.tests.smokeTest = runCommand "test-sgrep" { } ''
+    expr='"<foo>" __ "</foo>"'
+    data="<foo>1</foo><bar>2</bar>"
+    ${sgrep}/bin/sgrep "$expr" <<<$data >$out
+    read result <$out
+    [[ $result = 1 ]]
+  '';
+
   meta = with lib; {
     homepage = "https://www.cs.helsinki.fi/u/jjaakkol/sgrep.html";
     description = "A grep for structured text formats such as XML";