Makes button option work

src/main/java/com/fathzer/jchess/bot/Option.java

@@ -11,7 +11,7 @@ public enum Type {
 
 	protected Option(String name, T defaultValue) {
 		super(defaultValue);
-		if (name==null || defaultValue==null) {
+		if (name==null) {
 			throw new IllegalArgumentException();
 		}
 		this.name = name;

src/main/java/com/fathzer/jchess/bot/options/ButtonOption.java

@@ -3,7 +3,6 @@
 import com.fathzer.jchess.bot.Option;
 
 //TODO Is it usefull?
-//FIXME it will never inform listener as value of Void type can't change
 public class ButtonOption extends Option<Void> {
 
 	public ButtonOption(String name) {
@@ -19,4 +18,9 @@ public Type getType() {
 	public boolean isValid(Void value) {
 		return true;
 	}
+
+	@Override
+	public void setValue(Void value) {
+		super.fireChange(value, value);
+	}
 }

src/main/java/com/fathzer/jchess/bot/options/ComboOption.java

@@ -9,7 +9,7 @@ public class ComboOption extends Option<String> {
 
 	public ComboOption(String name, String defaultValue, Set<String> values) {
 		super(name, defaultValue);
-		if (!values.contains(defaultValue) || values.isEmpty()) {
+		if (defaultValue==null || !values.contains(defaultValue)) {
 			throw new IllegalArgumentException();
 		}
 		this.values = values;

src/main/java/com/fathzer/util/Observable.java

@@ -0,0 +1,35 @@
+package com.fathzer.util;
+
+import java.util.Collection;
+import java.util.LinkedList;
+import java.util.function.BiConsumer;
+
+public class Observable<T> {
+	private Collection<BiConsumer<T,T>> listeners;
+	private T value;
+
+	public Observable(T value) {
+		this.value = value;
+		this.listeners = new LinkedList<>();
+	}
+
+	public void addListener(BiConsumer<T,T> listener) {
+		this.listeners.add(listener);
+	}
+
+	public void setValue(T value) {
+		if (!this.value.equals(value)) {
+			final T previous = this.value;
+			this.value = value;
+			fireChange(previous, value);
+		}
+	}
+
+	protected void fireChange(final T previous, T value) {
+		listeners.forEach(c -> c.accept(previous, value));
+	}
+
+	public T getValue() {
+		return this.value;
+	}
+}

src/test/java/com/fathzer/jchess/bot/options/OptionsTest.java

@@ -3,6 +3,7 @@
 import static org.junit.jupiter.api.Assertions.*;
 
 import java.util.Set;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.BiConsumer;
 
 import org.junit.jupiter.api.Test;
@@ -25,6 +26,7 @@ public void accept(T t, T u) {
 	void testCombo() {
 		final Set<String> abSet = Set.of("a","b");
 		assertThrows(IllegalArgumentException.class, () -> new ComboOption("combo", "c", abSet));
+		assertThrows(IllegalArgumentException.class, () -> new ComboOption("combo", null, abSet));
 		assertThrows(IllegalArgumentException.class, () -> new ComboOption(null, "a", abSet));
 		final Option<String> combo = new ComboOption("combo", "a", Set.of("a","b"));
 		assertEquals("a", combo.getValue());
@@ -118,6 +120,17 @@ void testCheck() {
 
 	@Test
 	void testButton() {
-		fail("Not Yet Implemented");
+		assertThrows(IllegalArgumentException.class, () -> new ButtonOption(null));
+		final ButtonOption button = new ButtonOption("button");
+		final AtomicBoolean called = new AtomicBoolean();
+		OptionListener<Void> listener = new OptionListener<>() {
+			@Override
+			public void accept(Void a, Void b) {
+				called.set(true);
+			}
+		};
+		button.addListener(listener);
+		button.setValue(null);
+		assertTrue(called.get());
 	}
 }