Add emu breakdown test for zero values

test/emu/nanos6/CMakeLists.txt

@@ -10,3 +10,5 @@ test_emu(ss-mismatch.c SHOULD_FAIL
   REGEX "thread [0-9]\\+ ended with 1 stacked nanos6 subsystems")
 test_emu(delayed-connect-ss.c)
 test_emu(switch-same-type.c)
+
+test_emu(breakdown-no-black.c BREAKDOWN)

test/emu/nanos6/breakdown-no-black.c

@@ -0,0 +1,51 @@
+/* Copyright (c) 2021-2023 Barcelona Supercomputing Center (BSC)
+ * SPDX-License-Identifier: GPL-3.0-or-later */
+
+#include <stdio.h>
+#include "common.h"
+#include "emu/emu_prv.h"
+#include "instr.h"
+#include "instr_nanos6.h"
+
+/* This test attempts to create holes in the breakdown trace by creating a
+ * thread that emits the first Nanos6 event later than the ovni thread execute
+ * event OHx. When the breakdown model is enabled, the output breakdown PRV
+ * trace should contain already a value for time=0, which is when OHx is
+ * emitted. We also test that on 6W[ we emit another non-zero state. 
+ *
+ *               .              .
+ *               OHx            6W[
+ * --------------x--------------x--------------> time
+ *               .              .
+ *               .              .
+ * breakdown ----A--------------B--------------
+ *               .              .
+ *
+ * We check that A and B are not emitting 0. */
+
+int
+main(void)
+{
+	instr_start(0, 1);
+
+	/* Match the PRV line in the trace */
+	FILE *f = fopen("match.sh", "w");
+	if (f == NULL)
+		die("fopen failed:");
+
+	/* Ensure non-zero for A (first event) */
+	fprintf(f, "grep ':%ld:%d:[^0][0-9]*$' ovni/nanos6-breakdown.prv\n",
+			get_delta(), PRV_NANOS6_BREAKDOWN);
+
+	instr_nanos6_worker_loop_enter();
+
+	/* And for B */
+	fprintf(f, "grep ':%ld:%d:[^0][0-9]*$' ovni/nanos6-breakdown.prv\n",
+			get_delta(), PRV_NANOS6_BREAKDOWN);
+
+	instr_nanos6_worker_loop_exit();
+
+	instr_end();
+
+	return 0;
+}