Implement command (no arg) (#4026)

* Implement  command (no arg)
https://redis.io/docs/latest/commands/command/

Adding it for completeness and as alternative to COMMAND INFO for Redis server prior 7.0.0.

COMMAND (no args) is available with Redis 2.x
COMMAND INFO is available since REDIS version 7.0.0

Relates to: #2922
Support COMMAND commands (#2922)
commit  : 3590438

Closes #793

* Update ControlCommandsTest.java

---------

Co-authored-by: M Sazzadul Hoque <7600764+sazzad16@users.noreply.github.com>

src/main/java/redis/clients/jedis/Jedis.java

@@ -8253,6 +8253,12 @@ public Map<String, CommandInfo> commandInfo(String... commands) {
     return CommandInfo.COMMAND_INFO_RESPONSE.build(connection.getOne());
   }
 
+  public Map<String, CommandInfo> command() {
+    checkIsInMultiOrPipeline();
+    connection.sendCommand(COMMAND);
+    return CommandInfo.COMMAND_INFO_RESPONSE.build(connection.getOne());
+  }
+
   public List<String> commandList() {
     checkIsInMultiOrPipeline();
     connection.sendCommand(COMMAND, LIST);

src/test/java/redis/clients/jedis/commands/jedis/ControlCommandsTest.java

@@ -501,6 +501,28 @@ public void commandGetKeys() {
     assertEquals(2, keySandFlags.get(0).getValue().size());
   }
 
+
+  @Test
+  public void commandNoArgs() {
+    Map<String, CommandInfo> infos = jedis.command();
+
+    assertThat(infos.size(), greaterThan(0));
+
+    CommandInfo getInfo = infos.get("get");
+    assertEquals(2, getInfo.getArity());
+    assertEquals(2, getInfo.getFlags().size());
+    assertEquals(1, getInfo.getFirstKey());
+    assertEquals(1, getInfo.getLastKey());
+    assertEquals(1, getInfo.getStep());
+
+    assertNull(infos.get("foo")); // non-existing command
+
+    CommandInfo setInfo = infos.get("set");
+    assertEquals(3, setInfo.getAclCategories().size());
+    assertEquals(0, setInfo.getTips().size());
+    assertEquals(0, setInfo.getSubcommands().size());
+  }
+
   @Test
   public void commandInfo() {
     Map<String, CommandInfo> infos = jedis.commandInfo("GET", "foo", "SET");