Add a minimalist test case for the os_type label

Author: polytypic

test/bin/mdx-test/expect/dune.inc

@@ -371,6 +371,18 @@
  (alias runtest)
  (action (diff ocaml-errors-ellipsis/test-case.md ocaml-errors-ellipsis.actual)))
 
+(rule
+ (target os_type.actual)
+ (deps (package mdx) (source_tree os_type))
+ (action
+  (with-stdout-to %{target}
+   (chdir os_type
+    (run ocaml-mdx test --output - test-case.md)))))
+
+(rule
+ (alias runtest)
+ (action (diff os_type/test-case.md os_type.actual)))
+
 (rule
  (target padding.actual)
  (deps (package mdx) (source_tree padding))

test/bin/mdx-test/expect/os_type/test-case.md

@@ -0,0 +1,13 @@
+Mdx can skip blocks based on `os_type`:
+
+```ocaml os_type<>Win32
+# #require "unix"
+# Unix.nice 0
+- : int = 0
+```
+
+```ocaml os_type=Win32
+# #require "unix"
+# Unix.nice 0
+Exception: Invalid_argument "Unix.nice not implemented".
+```