Fixes for destiny bond

Plugins/PkmnLib.Plugin.Gen7.Tests/Scripts/Moves/DestinyBondTests.cs

@@ -70,6 +70,45 @@ public class DestinyBondTests
         await Assert.That(userVolatile.Contains(ScriptUtils.ResolveName<DestinyBondEffect>())).IsTrue();
     }
 
+    /// <summary>
+    /// Bulbapedia (Generation VII): Destiny Bond "will always fail if it was successfully executed on the
+    /// previous turn." A user that still carries the <see cref="DestinyBondEffect"/> from the previous use
+    /// fails the move. The <see cref="IScriptFailMove"/> hook runs before the effect is removed by the
+    /// user's move, so the lingering effect is what marks the consecutive use.
+    /// </summary>
+    [Test]
+    public async Task FailMove_UserStillDestinyBound_FailsMove()
+    {
+        // Arrange
+        var (script, move, _, userVolatile) = CreateTestSetup();
+        userVolatile.Add(new DestinyBondEffect());
+        var fail = false;
+
+        // Act
+        script.FailMove(move, ref fail);
+
+        // Assert
+        await Assert.That(fail).IsTrue();
+    }
+
+    /// <summary>
+    /// Bulbapedia (Generation VII): the move only fails "if it was successfully executed on the previous
+    /// turn." Without a lingering <see cref="DestinyBondEffect"/> on the user, the move executes normally.
+    /// </summary>
+    [Test]
+    public async Task FailMove_UserNotDestinyBound_DoesNotFailMove()
+    {
+        // Arrange
+        var (script, move, _, _) = CreateTestSetup();
+        var fail = false;
+
+        // Act
+        script.FailMove(move, ref fail);
+
+        // Assert
+        await Assert.That(fail).IsFalse();
+    }
+
     /// <summary>
     /// Bulbapedia: "if the user faints as the direct result of an attack, the attacking Pokémon also
     /// faints." When the Destiny Bound user faints from move damage, the attacker takes damage far in

Plugins/PkmnLib.Plugin.Gen7/Scripts/Moves/DestinyBond.cs

@@ -3,11 +3,20 @@ using PkmnLib.Plugin.Gen7.Scripts.Pokemon;
 namespace PkmnLib.Plugin.Gen7.Scripts.Moves;
 
 [Script(ScriptCategory.Move, "destiny_bond")]
-public class DestinyBond : Script, IScriptOnSecondaryEffect
+public class DestinyBond : Script, IScriptOnSecondaryEffect, IScriptFailMove
 {
     /// <inheritdoc />
     public void OnSecondaryEffect(IExecutingMove move, IPokemon target, byte hit)
     {
         move.User.Volatile.Add(new DestinyBondEffect());
     }
+
+    public void FailMove(IExecutingMove move, ref bool fail)
+    {
+        if (move.User.Volatile.Contains<DestinyBondEffect>())
+        {
+            fail = true;
+            move.User.Volatile.Remove<DestinyBondEffect>();
+        }
+    }
 }