fixup! CP-47001: [xapi-fdcaps]: add properties module and tests

lib/xapi-fdcaps/test/properties.t

@@ -2,22 +2,48 @@ Check that we get compile errors when trying to use a read-only or write-only pr
 
   $ cat >t.ml <<'EOF'
   > open Xapi_fdcaps.Properties
-  > let _ = as_readable (make `wronly `reg) in ()
+  > let _ = as_readable (make `wronly `reg)
   > EOF
   $ ocamlfind ocamlc -package xapi-fdcaps -c t.ml
-  File "t.ml", line 2, characters 40-42:
-  2 | let _ = as_readable (make `wronly `reg) in ()
-                                              ^^
-  Error: Syntax error
+  File "t.ml", line 2, characters 20-39:
+  2 | let _ = as_readable (make `wronly `reg)
+                          ^^^^^^^^^^^^^^^^^^^
+  Error: This expression has type
+           ([< Xapi_fdcaps.Properties.rw > `wronly ] as 'a,
+            [< Xapi_fdcaps.Properties.kind > `reg ] as 'b)
+           Xapi_fdcaps.Properties.t = ('a, 'b) Xapi_fdcaps.Properties.props
+         but an expression was expected of type
+           ([< Xapi_fdcaps.Properties.readable ] as 'c,
+            [< Xapi_fdcaps.Properties.kind ] as 'd)
+           Xapi_fdcaps.Properties.t = ('c, 'd) Xapi_fdcaps.Properties.props
+         Type
+           [< Xapi_fdcaps.Properties.rw > `wronly ] =
+             [< `rdonly | `rdwr | `wronly > `wronly ]
+         is not compatible with type
+           [< Xapi_fdcaps.Properties.readable ] = [< `rdonly | `rdwr ] 
+         The second variant type does not allow tag(s) `wronly
   [2]
 
   $ cat >t.ml <<'EOF'
   > open Xapi_fdcaps.Properties
-  > let _ = as_writable (make `rdonly `reg) in ()
+  > let _ = as_writable (make `rdonly `reg)
   > EOF
   $ ocamlfind ocamlc -package xapi-fdcaps -c t.ml
-  File "t.ml", line 2, characters 40-42:
-  2 | let _ = as_writable (make `rdonly `reg) in ()
-                                              ^^
-  Error: Syntax error
+  File "t.ml", line 2, characters 20-39:
+  2 | let _ = as_writable (make `rdonly `reg)
+                          ^^^^^^^^^^^^^^^^^^^
+  Error: This expression has type
+           ([< Xapi_fdcaps.Properties.rw > `rdonly ] as 'a,
+            [< Xapi_fdcaps.Properties.kind > `reg ] as 'b)
+           Xapi_fdcaps.Properties.t = ('a, 'b) Xapi_fdcaps.Properties.props
+         but an expression was expected of type
+           ([< Xapi_fdcaps.Properties.writable ] as 'c,
+            [< Xapi_fdcaps.Properties.kind ] as 'd)
+           Xapi_fdcaps.Properties.t = ('c, 'd) Xapi_fdcaps.Properties.props
+         Type
+           [< Xapi_fdcaps.Properties.rw > `rdonly ] =
+             [< `rdonly | `rdwr | `wronly > `rdonly ]
+         is not compatible with type
+           [< Xapi_fdcaps.Properties.writable ] = [< `rdwr | `wronly ] 
+         The second variant type does not allow tag(s) `rdonly
   [2]