Seed the random number generator before running each test. We use the…

… C RNG utilities because this is a C library and most of the test code is written in C.

tests/src/helpers.h

@@ -8,6 +8,7 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <limits.h>
+#include <time.h>
 
 #if !(defined(UDPARD_VERSION_MAJOR) && defined(UDPARD_VERSION_MINOR))
 #    error "Library version not defined"
@@ -158,6 +159,18 @@ static inline struct UdpardMemoryDeleter instrumentedAllocatorMakeMemoryDeleter(
     return out;
 }
 
+static inline void seedRandomNumberGenerator(void)
+{
+    unsigned          seed    = (unsigned) time(NULL);
+    const char* const env_var = getenv("RANDOM_SEED");
+    if (env_var != NULL)
+    {
+        seed = (unsigned) atoll(env_var);  // Conversion errors are possible but ignored.
+    }
+    srand(seed);
+    (void) fprintf(stderr, "RANDOM_SEED=%u\n", seed);
+}
+
 #ifdef __cplusplus
 }
 #endif

tests/src/test_misc.cpp

@@ -4,6 +4,7 @@
 /// SPDX-License-Identifier: MIT
 
 #include <udpard.h>
+#include "helpers.h"
 #include "hexdump.hpp"
 #include <unity.h>
 #include <iostream>
@@ -67,7 +68,10 @@ void testGather()
 }
 }  // namespace
 
-void setUp() {}
+void setUp()
+{
+    seedRandomNumberGenerator();  // Re-seed the RNG for each test to avoid coupling.
+}
 
 void tearDown() {}