Expand error release and handler test coverage

tests/err_unhandled_null.c

@@ -0,0 +1,61 @@
+#include "akerror.h"
+#include "err_capture.h"
+#include <unistd.h>
+#include <sys/wait.h>
+
+/*
+ * The default unhandled-error handler is the library's last stop: it exits the
+ * process. Both of its exits were untested -- exit(1) for a NULL context (a
+ * handler invoked with no error at all) and exit(errctx->status) for a real one.
+ *
+ * The handler never returns, so each case runs in a forked child and the test
+ * asserts the exact exit status. That is stricter than a WILL_FAIL test, which
+ * would pass on any non-zero exit, including one caused by an unrelated bug.
+ */
+
+/*
+ * Run the default handler on ctx in a child process and return the child's exit
+ * status, or -1 if it did not exit normally. The _exit() sentinel catches a
+ * handler that returns instead of terminating.
+ */
+static int handler_exit_status(akerr_ErrorContext *ctx)
+{
+    pid_t pid = fork();
+    if ( pid == 0 ) {
+	akerr_default_handler_unhandled_error(ctx);
+	_exit(99);
+    }
+    int status = 0;
+    if ( pid < 0 || waitpid(pid, &status, 0) != pid || !WIFEXITED(status) ) {
+	return -1;
+    }
+    return WEXITSTATUS(status);
+}
+
+int main(void)
+{
+    akerr_capture_install();
+    akerr_init();
+
+    /* No context to report: the handler has nothing to exit with but failure. */
+    AKERR_CHECK(handler_exit_status(NULL) == 1);
+
+    /*
+     * With a context, the status becomes the exit code. waitpid only reports
+     * its low 8 bits, which is where AKERR_VALUE (144) lands, and it is neither
+     * 0 nor the 1 used for the NULL case, so the two exits stay distinguishable.
+     */
+    akerr_ErrorContext *slot = akerr_next_error();
+    AKERR_CHECK(slot != NULL);
+    slot->refcount = 1;
+    slot->status = AKERR_VALUE;
+    AKERR_CHECK((AKERR_VALUE & 0xff) != 0 && (AKERR_VALUE & 0xff) != 1);
+    AKERR_CHECK(handler_exit_status(slot) == (AKERR_VALUE & 0xff));
+
+    slot = akerr_release_error(slot);
+    AKERR_CHECK(slot == NULL);
+    AKERR_CHECK(akerr_slots_in_use() == 0);
+
+    fprintf(stderr, "err_unhandled_null ok\n");
+    return 0;
+}