ocamltest: add the cd builtin action

This gives tests control over ocamltest's current working directory

ocamltest/builtin_actions.ml

@@ -37,6 +37,19 @@ let fail = make
     let result = Result.fail_with_reason "The fail action always fails." in
     (result, env))
 
+let cd = make
+  "cd"
+  (fun _log env ->
+    let cwd = Environments.safe_lookup Builtin_variables.cwd env in
+    begin
+      try
+        Sys.chdir cwd; (Result.pass, env)
+      with _ ->
+        let reason = "Could not chidir to \"" ^ cwd ^ "\"" in
+        let result = Result.fail_with_reason reason in
+        (result, env)
+    end)    
+
 let dumpenv = make
   "dumpenv"
   (fun log env ->
@@ -140,6 +153,7 @@ let _ =
     pass;
     skip;
     fail;
+    cd;
     dumpenv;
     libunix;
     libwin32unix;

ocamltest/builtin_variables.ml

@@ -27,6 +27,9 @@ open Variables (* Should not be necessary with a ppx *)
 let arguments = make ("arguments",
   "Arguments passed to executed programs and scripts")
 
+let cwd = make ("cwd",
+  "Used to change current working directory, but not updated")
+
 let exit_status = make ("exit_status",
   "Expected program exit status")
 
@@ -96,6 +99,7 @@ let test_fail = make ("TEST_FAIL",
 let _ = List.iter register_variable
   [
     arguments;
+    cwd;
     exit_status;
     files;
     ocamltest_response;

ocamltest/builtin_variables.mli

@@ -19,6 +19,8 @@
 
 val arguments : Variables.t
 
+val cwd : Variables.t
+
 val exit_status : Variables.t
 
 val files : Variables.t