fix(test): disale mdx when libextism isn't found

dune

@@ -3,4 +3,5 @@
 (mdx
  (package extism)
  (libraries extism-manifest extism yojson)
+ (enabled_if (not (= %{env:EXTISM_TEST_NO_LIB=} "1")))
  (deps wasm/code.wasm))

extism.opam

@@ -38,5 +38,5 @@ build: [
   ]
 ]
 dev-repo: "git+https://github.com/extism/ocaml-sdk.git"
-build-env: [EXTISM_TEST_NO_LIB = ""]
+build-env: [EXTISM_TEST_NO_LIB = "1"]
 post-messages: ["See https://extism.org/docs/install/ for information about installing libextism"]

extism.opam.template

@@ -1,2 +1,2 @@
-build-env: [EXTISM_TEST_NO_LIB = ""]
+build-env: [EXTISM_TEST_NO_LIB = "1"]
 post-messages: ["See https://extism.org/docs/install/ for information about installing libextism"]

src/bindings.ml

@@ -35,8 +35,8 @@ let locate () =
         exit n
       in
       match Sys.getenv_opt "EXTISM_TEST_NO_LIB" with
-      | None -> fail 1
-      | Some _ -> fail 0)
+      | Some "1" -> fail 0
+      | _ -> fail 1)
 
 let from =
   let filename = locate () in
@@ -181,5 +181,4 @@ let extism_plugin_cancel =
   fn "extism_plugin_cancel" (ptr void @-> returning bool)
 
 let extism_plugin_id = fn "extism_plugin_id" (ptr void @-> returning (ptr char))
-
 let extism_plugin_reset = fn "extism_plugin_reset" (ptr void @-> returning bool)

src/dune

@@ -11,4 +11,5 @@
  (libraries extism-manifest extism yojson)
  (package extism)
  (deps test/code.wasm)
+ (enabled_if (not (= %{env:EXTISM_TEST_NO_LIB=} "1")))
  (files :standard - *.mli))