Add query command tests.

Not a lot of variation in these commands, but the output is a little
difficult to write robust tests for because it's all stringly typed.
These tests will break pretty hard (or require lots of adapting) if we
introduce i18n.

The tests don't cover tab completion. That will have to come later.

src/test/java/org/mobarena/stats/command/GlobalStatsCommandTest.java

@@ -0,0 +1,49 @@
+package org.mobarena.stats.command;
+
+import com.garbagemule.MobArena.Messenger;
+import com.garbagemule.MobArena.framework.ArenaMaster;
+import org.bukkit.command.CommandSender;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mobarena.stats.MobArenaStats;
+import org.mobarena.stats.store.GlobalStats;
+import org.mobarena.stats.store.StatsStore;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import static org.hamcrest.CoreMatchers.*;
+import static org.hamcrest.MatcherAssert.*;
+import static org.mockito.Mockito.*;
+
+@ExtendWith(MockitoExtension.class)
+class GlobalStatsCommandTest {
+
+    MobArenaStats plugin;
+    GlobalStatsCommand subject;
+
+    @BeforeEach
+    void setup() {
+        plugin = mock(MobArenaStats.class);
+        subject = new GlobalStatsCommand(plugin);
+    }
+
+    @Test
+    void success() {
+        ArenaMaster am = mock(ArenaMaster.class);
+        CommandSender sender = mock(CommandSender.class);
+        String[] args = {};
+        Messenger messenger = mock(Messenger.class);
+        StatsStore store = mock(StatsStore.class);
+        GlobalStats stats = new GlobalStats(1, 2, 3, 4);
+        when(am.getGlobalMessenger()).thenReturn(messenger);
+        when(plugin.getStatsStore()).thenReturn(store);
+        when(plugin.getAsyncExecutor()).thenReturn(Runnable::run);
+        when(store.getGlobalStats()).thenReturn(stats);
+
+        boolean result = subject.execute(am, sender, args);
+
+        assertThat(result, equalTo(true));
+        verify(messenger).tell(eq(sender), contains("Global stats"));
+    }
+
+}