lib/os+dirs tests: hand-main plumbing -> assert (@test conversion B6)

WW_TEST_* env arrangement logic untouched; only the fail/exit plumbing
converts.

lib/os/ostest.ww

@@ -5,11 +5,9 @@
 // cover alloc/free; the direct row here pins the FFI shape under
 // lib/os itself so future bindings refactors can't quietly drift.
 //
-// Convention follows the stdlib `_run` test fixtures: hand-rolled
-// @test fns dispatched from `main()` in numeric order, with a
-// `signalled` global the main fn bumps so a failing case exits with
-// `WEXITSTATUS = signalled + 10` — the harness then knows which
-// scenario tripped. Same shape as temptest / shlextest / fnmatchtest.
+// Hand-rolled @test fns dispatched from `main()` in source order; a
+// failing case aborts via the assert/abort builtin (task #5 @test
+// conversion).
 //
 // Pre-arranged env state (set by 974_getenv_run.c via setenv/unsetenv
 // before exec'ing `ww run lib/os/ostest.ww`):
@@ -20,17 +18,15 @@
 //
 // Don't `use io;` here — lib/os and lib/io both export read/write/
 // close as C symbols that collide under the driver's flat-scope
-// concat (task #17). os alone is sufficient: getenv + exit are the
-// only primitives needed.
+// concat (task #17). os alone is sufficient: getenv + alloc/free are
+// the only primitives needed.
 
 package os_test;
 
 import os;
 import rt;
 
-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; };
@@ -47,9 +43,9 @@ fn streq(a: str, b: str) bool = {
 @test fn test_getenv_set() void = {
 	let r = os.getenv("WW_TEST_GETENV");
 	match (r) {
-	case void => fail();
+	case void => abort();
 	case let s: str => {
-		if (!streq(s, "hello-world")) { fail(); };
+		assert(!(!streq(s, "hello-world")));
 	};
 	};
 };
@@ -63,9 +59,9 @@ fn streq(a: str, b: str) bool = {
 @test fn test_getenv_empty() void = {
 	let r = os.getenv("WW_TEST_EMPTY");
 	match (r) {
-	case void => fail();
+	case void => abort();
 	case let s: str => {
-		if (s.len != 0) { fail(); };
+		assert(!(s.len != 0));
 	};
 	};
 };
@@ -76,7 +72,7 @@ fn streq(a: str, b: str) bool = {
 	let r = os.getenv("WW_TEST_NOT_SET");
 	match (r) {
 	case void => {};
-	case let s: str => fail();
+	case let s: str => abort();
 	};
 };
 
@@ -91,7 +87,7 @@ fn streq(a: str, b: str) bool = {
 	let r = os.getenv("WW_TEST_GETEN");
 	match (r) {
 	case void => {};
-	case let s: str => fail();
+	case let s: str => abort();
 	};
 };
 
@@ -106,16 +102,16 @@ fn streq(a: str, b: str) bool = {
 	p.len = 4096;
 	p[0] = 90u8;		// 0x5a
 	p[4095] = 165u8;	// 0xa5
-	if (p[0] != 90u8) { fail(); };
-	if (p[4095] != 165u8) { fail(); };
+	assert(!(p[0] != 90u8));
+	assert(!(p[4095] != 165u8));
 	os.free(p.ptr: *void, 4096u64);
 };
 
 export fn main() i32 = {
-	signalled = 1; test_getenv_set();
-	signalled = 2; test_getenv_empty();
-	signalled = 3; test_getenv_unset();
-	signalled = 4; test_getenv_prefix_no_match();
-	signalled = 5; test_alloc_free_roundtrip();
+	test_getenv_set();
+	test_getenv_empty();
+	test_getenv_unset();
+	test_getenv_prefix_no_match();
+	test_alloc_free_roundtrip();
 	return 0;
 };