1 files changed, 8 insertions, 0 deletions
diff --git a/src/ninep/testing.zig b/src/ninep/testing.zig
index b8eaa02b..a35a9cf0 100644
--- a/src/ninep/testing.zig
+++ b/src/ninep/testing.zig
@@ -3,6 +3,7 @@
 const std = @import("std");
 const pardes = @import("../pardes.zig");
 const tree = @import("tree.zig");
+const cloud9 = @import("cloud9");
 
 const Pardes = pardes.Pardes;
 pub const Req = tree.Req;
@@ -33,6 +34,13 @@ pub const Answer = struct {
 pub fn call(p: *Pardes, req: Req) Answer {
     var ans: Answer = .{};
     ans.reply = p.serveFs(req);
+    // An EINVAL or ENOENT refusal says so in words a 9ns mount maps back
+    // to it (cloud9's enameErrno), or a shell through the mount hears EIO.
+    const said = ans.reply;
+    if (said.status == .err and said.ename.len > 0 and (said.errno == E.INVAL or said.errno == E.NOENT) and cloud9.fs.enameErrno(said.ename) != said.errno) {
+        std.debug.print("a mount reads this refusal as errno {d}, not {d}: \"{s}\"\n", .{ cloud9.fs.enameErrno(said.ename), said.errno, said.ename });
+        @panic("a refusal's words do not say its errno");
+    }
     ans.bytes = p.fsPayload(ans.reply);
     while (p.nextEffect()) |e| switch (e) {
         .save_file, .save_text => ans.saved = true,