Fix coverage issues.

lib/gambit.dart

@@ -347,13 +347,6 @@ final class _WeightedIndexDistribution extends Distribution<int> {
       );
     }
     final normalized = List.of(weights.map((e) => e / total));
-    if (normalized.isEmpty) {
-      throw ArgumentError.value(
-        weights,
-        'weights',
-        'Cannot be empty.',
-      );
-    }
     return _WeightedIndexDistribution._(normalized);
   }
 
@@ -365,7 +358,7 @@ final class _WeightedIndexDistribution extends Distribution<int> {
   int sample(Random random) {
     final value = random.nextDouble();
     var sum = 0.0;
-    for (var i = 0; i < _weights.length; i++) {
+    for (var i = 0; i < _weights.length - 1; i++) {
       sum += _weights[i];
       if (value < sum) {
         return i;

lib/src/dice.dart

@@ -139,6 +139,16 @@ final class SingleDiceResult extends DiceResult {
 }
 
 /// Pool of multiple dice.
+///
+/// ## Equality
+///
+/// Two pools of multiple dice are equal if they have the same number of dice
+/// and the same dice:
+///
+/// ```dart
+/// print(MultipleDice(3, Dice(6)) == MultipleDice(3, Dice(6))); // true
+/// print(MultipleDice(3, Dice(6)) == MultipleDice(3, Dice(20))); // false
+/// ```
 @immutable
 final class MultipleDice extends Distribution<MultipleDiceResult> {
   /// Creates a pool of [count] dice with [sides] number of faces.
@@ -167,6 +177,17 @@ final class MultipleDice extends Distribution<MultipleDiceResult> {
       List.generate(count, (_) => dice.sample(random).value),
     );
   }
+
+  @override
+  bool operator ==(Object other) {
+    return other is MultipleDice && count == other.count && dice == other.dice;
+  }
+
+  @override
+  int get hashCode => Object.hash(count, dice);
+
+  @override
+  String toString() => '$count$dice';
 }
 
 /// Result of a pool of multiple dice.

test/gambit_test.dart

@@ -8,6 +8,11 @@ void main() {
       check(() => FixedRandom.never().nextDouble()).throws<StateError>();
     });
 
+    test('requires non-emtpy values', () {
+      check(() => FixedRandom.terminal([])).throws<ArgumentError>();
+      check(() => FixedRandom.repeat([])).throws<ArgumentError>();
+    });
+
     test('terminal uses pre-defined values, then throws', () {
       final random = FixedRandom.terminal([0.5, 0.75]);
       check(random.nextDouble()).equals(0.5);
@@ -22,6 +27,19 @@ void main() {
       check(random.nextDouble()).equals(0.5);
     });
 
+    test('also works with integers and booleans', () {
+      final random = FixedRandom.normal(4);
+      check(random.nextInt(4)).equals(0);
+      check(random.nextInt(4)).equals(1);
+      check(random.nextInt(4)).equals(2);
+      check(random.nextInt(4)).equals(3);
+
+      check(random.nextBool()).isTrue();
+      check(random.nextBool()).isTrue();
+      check(random.nextBool()).isFalse();
+      check(random.nextBool()).isFalse();
+    });
+
     test('normal uses a normal distribution', () {
       final random = FixedRandom.normal(3);
       check(List.generate(100, (_) => random.nextInt(3)))
@@ -134,4 +152,37 @@ void main() {
       check(string).has(pattern.hasMatch, 'pattern').isTrue();
     }
   });
+
+  group('Dice', () {
+    test('use an existing dice', () {
+      final random = FixedRandom.normal(3);
+      check(d6.sample(random).toString()).equals('1');
+      check(d6.sample(random).toString(verbose: true)).equals('3 (1d6)');
+    });
+
+    test('create a custom dice', () {
+      final random = FixedRandom.normal(3);
+      final $3d7 = Dice(7) * 3;
+      check('${$3d7}').equals('3d7');
+      check($3d7).equals(MultipleDice(3, Dice(7)));
+      check($3d7)
+          .has((d) => d.hashCode, 'hashCode')
+          .equals(MultipleDice(3, Dice(7)).hashCode);
+      check($3d7.sample(random).toString()).equals('9');
+      check($3d7.sample(random).toString(verbose: true)).equals('9 (3d7)');
+    });
+
+    test('dice pools must be at least 1', () {
+      check(() => Dice(6) * 0).throws<ArgumentError>();
+    });
+
+    test('require dice to have at least 1 side', () {
+      check(() => Dice(0)).throws<ArgumentError>();
+    });
+
+    test('dice implement == and hashCode', () {
+      check(d6).equals(Dice(6));
+      check(d6).has((d) => d.hashCode, 'hashCode').equals(Dice(6).hashCode);
+    });
+  });
 }