fix: return empty array if the transaction is empty (#349)

lib/redis_client/cluster/transaction.rb

@@ -8,6 +8,7 @@ class Cluster
     class Transaction
       ConsistencyError = Class.new(::RedisClient::Error)
       MAX_REDIRECTION = 2
+      EMPTY_ARRAY = [].freeze
 
       def initialize(router, command_builder, node: nil, slot: nil, asking: false)
         @router = router
@@ -62,10 +63,10 @@ def call_once_v(command, &block)
       def execute
         @pending_commands.each(&:call)
 
-        raise ArgumentError, 'empty transaction' if @pipeline._empty?
+        return EMPTY_ARRAY if @pipeline._empty?
         raise ConsistencyError, "couldn't determine the node: #{@pipeline._commands}" if @node.nil?
 
-        settle
+        commit
       end
 
       private
@@ -92,8 +93,17 @@ def prepare_tx
         @pending_commands.clear
       end
 
-      def settle
+      def commit
         @pipeline.call('EXEC')
+        settle
+      end
+
+      def cancel
+        @pipeline.call('DISCARD')
+        settle
+      end
+
+      def settle
         # If we needed ASKING on the watch, we need ASKING on the multi as well.
         @node.call('ASKING') if @asking
         # Don't handle redirections at this level if we're in a watch (the watcher handles redirections

test/redis_client/test_cluster.rb

@@ -224,11 +224,22 @@ def test_transaction_with_multiple_key
         end
       end
 
-      def test_transaction_with_empty_block
-        assert_raises(ArgumentError) { @client.multi {} }
+      def test_transaction_without_block
         assert_raises(LocalJumpError) { @client.multi }
       end
 
+      def test_transaction_with_empty_block
+        @captured_commands.clear
+        assert_empty(@client.multi {})
+        assert_empty(@captured_commands.to_a.map(&:command).map(&:first))
+      end
+
+      def test_transaction_with_empty_block_and_watch
+        @captured_commands.clear
+        assert_empty(@client.multi(watch: %w[key]) {})
+        assert_equal(%w[WATCH MULTI EXEC], @captured_commands.to_a.map(&:command).map(&:first))
+      end
+
       def test_transaction_with_only_keyless_commands
         assert_raises(::RedisClient::Cluster::Transaction::ConsistencyError) do
           @client.multi do |t|