Prüfsumme und wiederholbarer Zufall

FNV-1a für Zustandsprüfsummen und SplitMix64 als einzige Zufallsquelle
des Kerns. Beide sind gegen veröffentlichte Referenzwerte geprüft.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

core/tests/rng.rs

@@ -0,0 +1,49 @@
+use grovewright_core::rng::Rng;
+
+#[test]
+fn matches_the_splitmix64_reference_values() {
+    let mut rng = Rng::new(0);
+    assert_eq!(rng.next_u64(), 0xE220_A839_7B1D_CDAF);
+    assert_eq!(rng.next_u64(), 0x6E78_9E6A_A1B9_65F4);
+    assert_eq!(rng.next_u64(), 0x06C4_5D18_8009_454F);
+}
+
+#[test]
+fn the_same_seed_gives_the_same_sequence() {
+    let mut a = Rng::new(2026);
+    let mut b = Rng::new(2026);
+    for _ in 0..1_000 {
+        assert_eq!(a.next_u64(), b.next_u64());
+    }
+}
+
+#[test]
+fn different_seeds_give_different_sequences() {
+    assert_ne!(Rng::new(1).next_u64(), Rng::new(2).next_u64());
+}
+
+#[test]
+fn below_stays_inside_the_bound() {
+    let mut rng = Rng::new(7);
+    for bound in [1u32, 2, 3, 10, 100, 1_000_000, u32::MAX] {
+        for _ in 0..1_000 {
+            assert!(rng.below(bound) < bound);
+        }
+    }
+}
+
+#[test]
+fn below_reaches_every_value_of_a_small_bound() {
+    let mut rng = Rng::new(99);
+    let mut seen = [false; 6];
+    for _ in 0..1_000 {
+        seen[rng.below(6) as usize] = true;
+    }
+    assert_eq!(seen, [true; 6]);
+}
+
+#[test]
+#[should_panic(expected = "bound must be greater than zero")]
+fn below_refuses_a_bound_of_zero() {
+    Rng::new(1).below(0);
+}