tests/qtest/npcm7xx_rng-test: dump random data on failure

Dump the collected random data after a randomness test failure.

Note that this relies on the test having called
g_test_set_nonfatal_assertions() so we don't abort immediately on the
assertion failure.

Signed-off-by: Havard Skinnemoen <hskinnemoen@google.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
[PMM: minor commit message tweak]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

tests/qtest/npcm7xx_rng-test.c

@@ -20,6 +20,7 @@
 
 #include "libqtest-single.h"
 #include "qemu/bitops.h"
+#include "qemu-common.h"
 
 #define RNG_BASE_ADDR   0xf000b000
 
@@ -36,6 +37,13 @@
 /* Number of bits to collect for randomness tests. */
 #define TEST_INPUT_BITS  (128)
 
+static void dump_buf_if_failed(const uint8_t *buf, size_t size)
+{
+    if (g_test_failed()) {
+        qemu_hexdump(stderr, "", buf, size);
+    }
+}
+
 static void rng_writeb(unsigned int offset, uint8_t value)
 {
     writeb(RNG_BASE_ADDR + offset, value);
@@ -188,6 +196,7 @@ static void test_continuous_monobit(void)
     }
 
     g_assert_cmpfloat(calc_monobit_p(buf, sizeof(buf)), >, 0.01);
+    dump_buf_if_failed(buf, sizeof(buf));
 }
 
 /*
@@ -209,6 +218,7 @@ static void test_continuous_runs(void)
     }
 
     g_assert_cmpfloat(calc_runs_p(buf.l, sizeof(buf) * BITS_PER_BYTE), >, 0.01);
+    dump_buf_if_failed(buf.c, sizeof(buf));
 }
 
 /*
@@ -230,6 +240,7 @@ static void test_first_byte_monobit(void)
     }
 
     g_assert_cmpfloat(calc_monobit_p(buf, sizeof(buf)), >, 0.01);
+    dump_buf_if_failed(buf, sizeof(buf));
 }
 
 /*
@@ -254,6 +265,7 @@ static void test_first_byte_runs(void)
     }
 
     g_assert_cmpfloat(calc_runs_p(buf.l, sizeof(buf) * BITS_PER_BYTE), >, 0.01);
+    dump_buf_if_failed(buf.c, sizeof(buf));
 }
 
 int main(int argc, char **argv)