--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test_snprintf.c	Wed Dec 03 03:04:39 2025 -0500
@@ -0,0 +1,74 @@
+#include "printf.h"
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <limits.h>
+#include <float.h>
+
+/* This is a smaller buffer size than test.h needs, because we want to test
+ * NUL-terminating behavior. */
+#define BUFSZ 128
+
+int test_snprintf(void)
+{
+	int n1, n2, b1, b2;
+	char s1[BUFSZ], s2[BUFSZ];
+
+	b1 = my_snprintf(NULL, 0,
+#include "test.h"
+		);
+	if (b1 < 0) {
+		fprintf(stderr, "my_snprintf(NULL, 0, ...): %s\n", my_strerror(b1));
+		return -1;
+	}
+
+	b2 = snprintf(NULL, 0,
+#include "test.h"
+		);
+	if (b2 < 0) {
+		perror("snprintf(NULL, 0, ...)");
+		return -1;
+	}
+
+	if (b1 != b2) {
+		fprintf(stderr, "snprintf and my_snprintf returned different buffer sizes!\n");
+		return -1;
+	}
+
+	n1 = my_snprintf(s1, BUFSZ,
+#include "test.h"
+		);
+	if (n1 < 0) {
+		fprintf(stderr, "my_snprintf: %s\n", my_strerror(n1));
+		return -1;
+	}
+	n2 = snprintf(s2, BUFSZ,
+#include "test.h"
+		);
+	if (n2 < 0) {
+		my_free(s1);
+		perror("snprintf");
+		return -1;
+	}
+
+	if (n1 != b1) {
+		fprintf(stderr, "my_snprintf with and without a buffer returned different results\n");
+		return -1;
+	}
+
+	if (n1 != n2) {
+		printf("snprintf and my_snprintf returned different buffer sizes\n");
+		return -1;
+	}
+
+	if (strcmp(s1, s2)) {
+		fprintf(stderr, "Got different results!!\n");
+		fprintf(stderr, " snprintf: %s", s1);
+		fprintf(stderr, " my_snprintf: %s", s2);
+
+		return -1;
+	}
+
+	return 0;
+}