feat: refactor testTxDiscard function to use MultiCommandTestCase

The `testTxDiscard` function in the `test_txn_9.go` file has been refactored to use the `MultiCommandTestCase` struct for executing multiple commands within a transaction. This change improves code readability and maintainability by encapsulating the commands and assertions within a single test case object.

internal/test_txn_9.go

@@ -0,0 +1,62 @@
+package internal
+
+import (
+	"github.com/codecrafters-io/redis-tester/internal/redis_executable"
+	resp_value "github.com/codecrafters-io/redis-tester/internal/resp/value"
+	"github.com/codecrafters-io/redis-tester/internal/resp_assertions"
+
+	"github.com/codecrafters-io/redis-tester/internal/instrumented_resp_connection"
+	"github.com/codecrafters-io/redis-tester/internal/test_cases"
+	"github.com/codecrafters-io/tester-utils/test_case_harness"
+)
+
+func testTxDiscard(stageHarness *test_case_harness.TestCaseHarness) error {
+	b := redis_executable.NewRedisExecutable(stageHarness)
+	if err := b.Run(); err != nil {
+		return err
+	}
+
+	logger := stageHarness.Logger
+
+	client, err := instrumented_resp_connection.NewFromAddr(stageHarness, "localhost:6379", "client1")
+	if err != nil {
+		logFriendlyError(logger, err)
+		return err
+	}
+	defer client.Close()
+
+	transactionTestCase := test_cases.TransactionTestCase{
+		CommandQueue: [][]string{
+			{"SET", "foo", "41"},
+			{"INCR", "foo"},
+		},
+		ResultArray: []resp_value.Value{},
+	}
+
+	if err := transactionTestCase.RunMulti(client, logger); err != nil {
+		return err
+	}
+
+	if err := transactionTestCase.RunQueueAll(client, logger); err != nil {
+		return err
+	}
+
+	multiCommandTestCase := test_cases.MultiCommandTestCase{
+		Commands: [][]string{
+			{"DISCARD"},
+			{"GET", "foo"},
+			{"DISCARD"},
+		},
+		Assertions: []resp_assertions.RESPAssertion{
+			resp_assertions.NewStringAssertion("OK"),
+			resp_assertions.NewNilAssertion(),
+			resp_assertions.NewErrorAssertion("ERR DISCARD without MULTI"),
+		},
+	}
+
+	if err := multiCommandTestCase.RunAll(client, logger); err != nil {
+		return err
+	}
+
+	return nil
+}

internal/tester_definition.go

@@ -192,6 +192,11 @@ var testerDefinition = tester_definition.TesterDefinition{
 			Slug:     "xu1",
 			TestFunc: testStreamsXreadBlockMaxID,
 		},
+		// ToDo: Slugs are placeholders
+		{
+			Slug:     "xv0",
+			TestFunc: testTxDiscard,
+		},
 		{
 			Slug:     "xv1",
 			TestFunc: testTxSuccess,