Add support for queuing commands within a transaction

course-definition.yml

@@ -3458,7 +3458,32 @@ stages:
     name: "Queueing commands"
     difficulty: medium
     description_md: |
-      **🚧 We're still working on instructions for this stage**. You can find notes on how the tester works below.
+      In this stage, you'll add support for queuing commands within a transaction.
+
+      ### Queuing commands
+
+      After [MULTI](https://redis.io/docs/latest/commands/multi/) is executed, any further commands
+      from a connection are queued until [EXEC](https://redis.io/docs/latest/commands/exec/) is executed.
+
+      The response to all of these commands is `+QUEUED\r\n` (That's `QUEUED` encoded as a [Simple String](https://redis.io/docs/latest/develop/reference/protocol-spec/#simple-strings)).
+
+      Example:
+
+      ```bash
+      $ redis-cli
+      > MULTI
+      OK
+      > SET foo 41
+      QUEUED
+      > INCR foo
+      QUEUED
+
+      ... (and so on, until EXEC is executed)
+      ```
+
+      When commands are queued, they should not be executed or alter the database in any way.
+
+      In the example above, until `EXEC` is executed, the key `foo` will not exist.
 
       ### Tests
 
@@ -3471,17 +3496,18 @@ stages:
       The tester will then connect to your server as a Redis client, and send multiple commands using the same connection:
 
       ```bash
-      $ redis-cli MULTI
-      > SET foo 41
-      > INCR foo
+      $ redis-cli
+      > MULTI
+      > SET foo 41 (expecting "+QUEUED\r\n")
+      > INCR foo (expecting "+QUEUED\r\n")
       ```
 
-      The tester will then create another connection to your master as a Redis client, and send a single command:
+      Since these commands were only "queued", the key `foo` should not exist yet. The tester will verify this by creating
+      another connection and sending this command:
 
       ```bash
-      $ redis-cli GET foo
+      $ redis-cli GET foo (expecting `$-1\r\n` as the response)
       ```
-
     marketing_md: |
       In this stage, you'll implement queueing commands to a transaction.