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Configure parallel tests in rails app (which doesn't work - yet) #78

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Configure parallel tests in rails app (which doesn't work - yet)
zcotter Mar 31, 2026
dc1dac7
Attempt prallelize setup
zcotter Apr 1, 2026
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1 change: 1 addition & 0 deletions rails_app/config/environments/test.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -42,4 +42,5 @@

# Log to STDOUT
config.logger = ActiveSupport::TaggedLogging.logger(STDOUT)
config.log_level = "error"
end
9 changes: 7 additions & 2 deletions rails_app/lib/temporal_client.rb
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Expand Up @@ -7,10 +7,15 @@ def self.instance

# Load config and apply defaults
args, kwargs = Temporalio::EnvConfig::ClientConfig.load_client_connect_options
args[0] ||= 'localhost:7233' # Default address
args[1] ||= 'default' # Default namespace

@instance = Temporalio::Client.connect(*args, **kwargs, logger: Rails.logger)
@instance = Temporalio::Client.connect(self.server_target, args[1], **kwargs, logger: Rails.logger)
end

def self.server_target
args, _kwargs = Temporalio::EnvConfig::ClientConfig.load_client_connect_options
server = args[0]
server || 'localhost:7233'
end

def self.instance=(instance)
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10 changes: 10 additions & 0 deletions rails_app/test/test_helper.rb
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Expand Up @@ -46,6 +46,16 @@ class TestCase

# Setup all fixtures in test/fixtures/*.yml for all tests in alphabetical order.
fixtures :all

parallelize(workers: :number_of_processors, threshold: 1)
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@chris-olszewski chris-olszewski Apr 1, 2026

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This doesn't work due to us not supporting using native backed Ruby structures across forks: https://ruby.temporal.io/#forking

This can be worked around by setting up a Temporal::Client for each process.

Suggested change
parallelize(workers: :number_of_processors, threshold: 1)
parallelize(workers: :number_of_processors, threshold: 1)
# Create a fresh runtime and client in each forked worker,
# connecting to the same dev server started in the parent.
parallelize_setup do |_worker|
TemporalClient.instance = Temporalio::Client.connect(
TemporalClient.server_target,
'default',
runtime: Temporalio::Runtime.new,
logger: Rails.logger
)
end

Note, this requires adding server_target getter/setter on the TemporalClient module in this sample.

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@zcotter zcotter Apr 1, 2026

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Thanks for the quick response @chris-olszewski ! I tried your sample code with parallelize_setup and I'm still encountering a few other issues:

  1. RuntimeError: Client already set
  2. Temporalio::Internal::Bridge::Error: Cannot create worker across forks (original runtime PID is 74216, current is 74376)
  3. The test suite freezes before finishing until i kill it

I pushed up the changes I made in case I got lost on the server_target implementation. Appreciate your help!

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@chris-olszewski chris-olszewski Apr 2, 2026

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Ah, I apologize. I accidentally was using a build of the gem where I was leaking all of the native owned resources (which avoids the issue in a very dumb way).

The Temporalio::Testing::WorkflowEnvironment creates a new Runtime which can't be shared across processes, so that in addition to the client need to be setup per process.
e.g.

    parallelize_setup do |_worker|
      @temporal_test_env = Temporalio::Testing::WorkflowEnvironment.start_local(logger: Rails.logger)
      TemporalClient.instance = @temporal_test_env.client
    end
    parallelize_teardown do |_worker|
      @temporal_test_env&.shutdown
    end

And remove the module level test server start (and the temporal_client.rs changes are no longer necessary).

I realize this isn't great as you're starting a dev server per-process, but it should prevent sharing any native backed objects across forks.

parallelize_setup do |_worker|
TemporalClient.instance = Temporalio::Client.connect(
TemporalClient.server_target,
'default',
runtime: Temporalio::Runtime.new,
logger: Rails.logger
)
end
end
end

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