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The test type PI Outbound allows to test a flow in which a SAP Backend (or other system) business document triggers the interface message and this message is processed in SAP PI/PO until the final version of an XML or flat file is ready to be sent out to the 3rd party receiver.
That’s why, in order to execute this type of testing you need to define a associated test case, that will trigger the message from a business document.
Alternatively, if the application interface is based on SAP Output Control, there is a single test case approach described here: Outbound test cases with triggering the Output Control.
During the test case execution, the PI outbound type will listen if particular message was processed in SAP PI/PO. If so, it would fetch the content and compare it with the reference.
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