AVRO-4275: [C] Strengthen test assertions to check EINVAL

Assert that the INT64_MIN block count tests fail with the specific
EINVAL error code rather than just any non-zero return. This ensures
the tests actually exercise the new guard rather than passing due to
an unrelated failure downstream.

Addresses review feedback on PR #3842.

Assisted-by: GitHub Copilot:claude-opus-4.6

Author: iemejia

lang/c/tests/test_avro_4275.c

@@ -30,6 +30,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <stdint.h>
+#include <errno.h>
 #include <avro.h>
 
 /*
@@ -118,20 +119,21 @@ static int test_array_int64min(void)
         return 1;
     }
 
-    /* This MUST fail gracefully (return error) rather than looping
-     * unboundedly or triggering undefined behavior. */
+    /* This MUST fail with EINVAL rather than looping unboundedly or
+     * triggering undefined behavior from negating INT64_MIN. */
     rc = avro_value_read(reader, &value);
-    if (rc == 0) {
+    if (rc != EINVAL) {
         fprintf(stderr,
-                "FAIL: INT64_MIN array block count was not rejected\n");
+                "FAIL: INT64_MIN array block count: expected EINVAL, "
+                "got rc=%d (%s)\n", rc, avro_strerror());
         avro_reader_free(reader);
         avro_value_decref(&value);
         avro_value_iface_decref(iface);
         avro_schema_decref(schema);
         return 1;
     }
 
-    printf("PASS: INT64_MIN array block count rejected: %s\n",
+    printf("PASS: INT64_MIN array block count rejected with EINVAL: %s\n",
            avro_strerror());
 
     avro_reader_free(reader);
@@ -183,19 +185,21 @@ static int test_map_int64min(void)
         return 1;
     }
 
-    /* This MUST fail gracefully. */
+    /* This MUST fail with EINVAL rather than looping unboundedly or
+     * triggering undefined behavior from negating INT64_MIN. */
     rc = avro_value_read(reader, &value);
-    if (rc == 0) {
+    if (rc != EINVAL) {
         fprintf(stderr,
-                "FAIL: INT64_MIN map block count was not rejected\n");
+                "FAIL: INT64_MIN map block count: expected EINVAL, "
+                "got rc=%d (%s)\n", rc, avro_strerror());
         avro_reader_free(reader);
         avro_value_decref(&value);
         avro_value_iface_decref(iface);
         avro_schema_decref(schema);
         return 1;
     }
 
-    printf("PASS: INT64_MIN map block count rejected: %s\n",
+    printf("PASS: INT64_MIN map block count rejected with EINVAL: %s\n",
            avro_strerror());
 
     avro_reader_free(reader);