tests: overhaul deterministic test randomness

The existing code provides two randomness mechanisms for test purposes:
- g_insecure_rand_ctx (with its wrappers InsecureRand*), which during tests is
  initialized using either zeros (SeedRand::ZEROS), or using environment-provided
  randomness (SeedRand::SEED).
- g_mock_deterministic_tests, which controls some (but not all) of the normal
  randomness output if set, but then makes it extremely predictable (identical
  output repeatedly).

Replace this with a single mechanism, which retains the SeedRand modes to control
all randomness. There is a new internal deterministic PRNG inside the random
module, which is used in GetRandBytes() when in test mode, and which is also used
to initialize g_insecure_rand_ctx. This means that during tests, all random numbers
are made deterministic. There is one exception, GetStrongRandBytes(), which even
in test mode still uses the normal PRNG state.

This probably opens the door to removing a lot of the ad-hoc "deterministic" mode
functions littered through the codebase (by simply running relevant tests in
SeedRand::ZEROS mode), but this isn't done yet.

1 files changed, 3 insertions, 17 deletions

diff --git a/src/test/util/random.h b/src/test/util/random.h
index 18ab425e48..09a475f8b3 100644
--- a/src/test/util/random.h
+++ b/src/test/util/random.h
@@ -19,27 +19,13 @@
  */
 extern FastRandomContext g_insecure_rand_ctx;
 
-/**
- * Flag to make GetRand in random.h return the same number
- */
-extern bool g_mock_deterministic_tests;
-
 enum class SeedRand {
     ZEROS, //!< Seed with a compile time constant of zeros
-    SEED,  //!< Call the Seed() helper
+    SEED,  //!< Use (and report) random seed from environment, or a (truly) random one.
 };
 
-/** Seed the given random ctx or use the seed passed in via an environment var */
-void Seed(FastRandomContext& ctx);
-
-static inline void SeedInsecureRand(SeedRand seed = SeedRand::SEED)
-{
-    if (seed == SeedRand::ZEROS) {
-        g_insecure_rand_ctx = FastRandomContext(/*fDeterministic=*/true);
-    } else {
-        Seed(g_insecure_rand_ctx);
-    }
-}
+/** Seed the RNG for testing. This affects all randomness, except GetStrongRandBytes(). */
+void SeedRandomForTest(SeedRand seed = SeedRand::SEED);
 
 static inline uint32_t InsecureRand32()
 {