lib/io tests: hand-main plumbing -> assert (@test conversion B5)

lib/errors/errnotest.ww

@@ -11,11 +11,6 @@ package errors_test;
 import errors;
 import os;
 
-// signalled — bumped by main before each test so a failing exit code
-// pinpoints the offending case.
-let signalled: i32 = 0;
-fn fail() void = { os.exit(signalled + 10); };
-
 fn streq(a: str, b: str) bool = {
 	if (a.len != b.len) { return false; };
 	let i: i32 = 0;
@@ -85,7 +80,7 @@ fn errtag(e: errors.error) int = {
 		// regardless — it is how errno is actually used (cf
 		// lib/io/stream.ww:53, and Hare's errors/rt.ha callers).
 		let er: errors.error = errors.errno(ins[i]);
-		if (errtag(er) != exp[i]) { fail(); };
+		assert(!(errtag(er) != exp[i]));
 		i += 1;
 	};
 };
@@ -94,25 +89,25 @@ fn errtag(e: errors.error) int = {
 @test fn opaquetail() void = {
 	// EIO (5) is outside the mapped set, so it wraps opaque_.
 	let e: errors.error = errors.errno(5);
-	if (errtag(e) != 99) { fail(); };
+	assert(!(errtag(e) != 99));
 	match (e) {
 	case let o: errors.opaque_ =>
-		if (!streq((*o.strerror)(&o.data), "Unknown error")) { fail(); };
+		assert(!(!streq((*o.strerror)(&o.data), "Unknown error")));
 	case =>
-		fail();
+		abort();
 	};
 };
 
 // ---- os.strerror mapped path --------------------------------------
 @test fn strerrortext() void = {
-	if (!streq(os.strerror(os.ENOENT), "No such file or directory")) { fail(); };
-	if (!streq(os.strerror(os.EINVAL), "Invalid argument")) { fail(); };
-	if (!streq(os.strerror(5), "Unknown error")) { fail(); };
+	assert(!(!streq(os.strerror(os.ENOENT), "No such file or directory")));
+	assert(!(!streq(os.strerror(os.EINVAL), "Invalid argument")));
+	assert(!(!streq(os.strerror(5), "Unknown error")));
 };
 
 export fn main() i32 = {
-	signalled = 1; mapping();
-	signalled = 2; opaquetail();
-	signalled = 3; strerrortext();
+	mapping();
+	opaquetail();
+	strerrortext();
 	return 0;
 };