start testing the public/circuit call API.

test/operation_test.rb

@@ -1,5 +1,32 @@
 require "test_helper"
 
+# Tests around {Operation.call}.
+class OperationTest < Minitest::Spec
+  class Noop < Trailblazer::Operation
+    def self.capture_circuit_options((ctx, flow_options), **circuit_options)
+      ctx[:capture_circuit_options] = circuit_options.keys.inspect
+
+      return Trailblazer::Activity::Right, [ctx, flow_options]
+    end
+
+    step task: method(:capture_circuit_options)
+  end
+
+  it "doesn't mistake circuit options as ctx variables when using circuit-interface" do
+    signal, (ctx, _) = Noop.call([{params: {}}, {}], variable_for_circuit_options: true) # call_with_public_interface
+    #@ {:variable_for_circuit_options} is not supposed to be in {ctx}.
+    assert_equal ctx.inspect, %({:params=>{}, :capture_circuit_options=>"[:variable_for_circuit_options, :exec_context, :activity, :runner]"})
+  end
+
+  it "doesn't mistake circuit options as ctx variables when using the call interface" do
+    result = Noop.call(params: {}, model: true, "current_user" => Object) # call with public interface.
+    #@ {:variable_for_circuit_options} is not supposed to be in {ctx}.
+    assert_equal result.inspect, %(<Result:true #<Trailblazer::Context::Container wrapped_options={:params=>{}, :model=>true, "current_user"=>Object} mutable_options={:capture_circuit_options=>"[:exec_context, :wrap_runtime, :activity, :runner]"}> >)
+  end
+end
+
+# TODO: remove this test as many cases are covered via autogenerated activity tests.
+
 class DeclarativeApiTest < Minitest::Spec
   it "doesn't invoke {call} twice when using public interface" do
     class MyOp < Trailblazer::Operation