Merge node fails to output data on false branch during test step

[antonlvovych]

Bug Description

When executing a workflow containing a Merge node, the output is inconsistent depending on how the test is performed. Specifically, when using the "Test step" feature on the Merge node, the output is correct on the first execution but fails on the second execution. This issue only occurs for the FALSE branch, while the TRUE branch behaves as expected.

Possibly related to #12436

To Reproduce

1. Open the workflow using the provided file: My_workflow.json
2. Select the Merge node and click on Test step.
3. Observe the output:
   • On the first execution, the Merge node outputs 1 item as expected.
     
   • On the second execution, the Merge node outputs nothing, which is incorrect.
     
4. Click Test workflow instead of Test step and observe that the output of the Merge node is correct (1 item).
5. Change the condition to go through the TRUE branch and repeat steps 2-4. The issue does not reproduce for the TRUE branch, and it consistently produces the output data on Test step.

Expected behavior

The Merge node should consistently output 1 item regardless of how many times Test step is executed. The output should not vary between the first and second execution, and the behavior should be identical for both the TRUE and FALSE branches.

Operating System

docker (self-hosted)

n8n Version

1.80.4

Node.js Version

20.18.3

Database

PostgreSQL

Execution mode

queue

[Joffcom]

Hey @antonlvovych,

We have created an internal ticket to look into this which we will be tracking as "GHC-999"

[Joffcom]

Hey @antonlvovych,

Interestingly I expect the merge node not to ever output data in the way you have it set up as it should always have the data in both inputs before moving on. I will pass this to the nodes team to resolve.

[antonlvovych]

@Joffcom if that’s the case, what would be the correct way to merge 2 inputs into 1 and continue the workflow regardless of which input arrives? I need the workflow to proceed with whichever branch completes and without waiting for both inputs.

Here is my workflow and it works just fine except "Test step" on Merge node in case of FALSE branch.

[Joffcom]

Hey @antonlvovych

The way I have always dealt with that is just put both paths into the same input so drop the merge and have the false and edit edit field node both go into the http request node then the node will loop over the items for both inputs as needed.

[antonlvovych]

@Joffcom thank you 🙌

[antonlvovych]

@Joffcom here is one more similar issue

Test workflow works just fine

If I try to run not the entire workflow, but only a code node with Test step - getting this error

[antonlvovych]

And for the Set node it's also buggy

Executing entire workflow with Test workflow

Executing just one step with Test step

No output data when executing Test step