Add some testing

src/test/java/org/bukkit/InstrumentTest.java

@@ -0,0 +1,15 @@
+package org.bukkit;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertThat;
+
+import org.junit.Test;
+
+public class InstrumentTest {
+    @Test
+    public void getByType() {
+        for (Instrument instrument : Instrument.values()) {
+            assertThat(Instrument.getByType(instrument.getType()), is(instrument));
+        }
+    }
+}