Fix omniscience effect for colorless mana.

Also unified the tests for omniscience into a single file, and
put the effect into a single class so that Tamiyo and Omniscience
can share implementations.

Mage/src/main/java/mage/abilities/effects/common/continuous/CastFromHandWithoutPayingManaCostEffect.java

@@ -0,0 +1,77 @@
+package mage.abilities.effects.common.continuous;
+
+import mage.MageObject;
+import mage.abilities.Ability;
+import mage.abilities.condition.CompoundCondition;
+import mage.abilities.condition.Condition;
+import mage.abilities.condition.common.SourceIsSpellCondition;
+import mage.abilities.costs.AlternativeCostSourceAbility;
+import mage.abilities.effects.ContinuousEffectImpl;
+import mage.cards.Card;
+import mage.cards.SplitCardHalf;
+import mage.constants.*;
+import mage.filter.common.FilterNonlandCard;
+import mage.game.Game;
+import mage.game.stack.Spell;
+import mage.players.Player;
+
+import java.util.UUID;
+
+public class CastFromHandWithoutPayingManaCostEffect extends ContinuousEffectImpl {
+
+    public CastFromHandWithoutPayingManaCostEffect() {
+        super(Duration.WhileOnBattlefield, Outcome.Detriment);
+        staticText = "You may cast nonland cards from your hand without paying their mana costs";
+    }
+
+    public CastFromHandWithoutPayingManaCostEffect(final CastFromHandWithoutPayingManaCostEffect effect) {
+        super(effect);
+    }
+
+    @Override
+    public CastFromHandWithoutPayingManaCostEffect copy() {
+        return new CastFromHandWithoutPayingManaCostEffect(this);
+    }
+
+    @Override
+    public boolean apply(Layer layer, SubLayer sublayer, Ability source, Game game) {
+        Player controller = game.getPlayer(source.getControllerId());
+        if (controller != null) {
+            controller.getAlternativeSourceCosts().add(new AlternativeCostSourceAbility(
+                    null, new CompoundCondition(SourceIsSpellCondition.getInstance(), new IsBeingCastFromHandCondition()), null, new FilterNonlandCard(), true));
+            return true;
+        }
+        return false;
+    }
+
+    @Override
+    public boolean apply(Game game, Ability source) {
+        return false;
+    }
+
+    @Override
+    public boolean hasLayer(Layer layer) {
+        return layer == Layer.RulesEffects;
+    }
+}
+
+class IsBeingCastFromHandCondition implements Condition {
+
+    @Override
+    public boolean apply(Game game, Ability source) {
+        MageObject object = game.getObject(source.getSourceId());
+        if (object instanceof SplitCardHalf) {
+            UUID splitCardId = ((Card) object).getMainCard().getId();
+            object = game.getObject(splitCardId);
+        }
+        if (object instanceof Spell) { // needed to check if it can be cast by alternate cost
+            Spell spell = (Spell) object;
+            return spell.getFromZone() == Zone.HAND;
+        }
+        if (object instanceof Card) { // needed for the check what's playable
+            Card card = (Card) object;
+            return game.getPlayer(card.getOwnerId()).getHand().get(card.getId(), game) != null;
+        }
+        return false;
+    }
+}