Proposed technique for mocking standalone functions from go-fastly by kpfleming · Pull Request #1686 · fastly/cli

kpfleming · 2026-03-11T19:14:33Z

THIS PR IS FOR DISCUSSION ONLY, IT IS NOT A COMPLETE IMPLEMENTATION.

Change summary

This demonstrates a possible technique for mocking 'new style' API functions in go-fastly that are not methods on the Client object. The techique requires a few things:

A new parameter to app.Run which allows tests to modify argparser.Command structs after they have been created but before test scenario execution begins. The explicit intent of this is for injecting a mock function into the command-to-be-tested's structure.
A CommandHook field in the testutil.CLIScenario struct which allows a scenario to indicate that it would like to inspect or modify the argparser.Command struct for the command that it tests.
New code in RunCLIScenario which detects the presence of a CommandHook in a scenario and then locates the relevant argparser.Command struct, passing it to the CommandHook.

Example implementations for two test scenarios for fastly compute acl create are included; one example demonstrates testing the content of
the input structure passed to the mock function.

This demonstrates a possible technique for mocking 'new style' API functions in go-fastly that are not methods on the Client object. The techique requires a few things: 1. A new parameter to app.Run which allows tests to modify argparser.Command structs after they have been created but before test scenario execution begins. The explicit intent of this is for injecting a mock function into the command-to-be-tested's structure. 2. A 'CommandHook' field in the testutil.CLIScenario struct which allows a scenario to indicate that it would like to inspect or modify the argparser.Command struct for the command that it tests. 3. New code in RunCLIScenario which detects the presence of a 'CommandHook' in a scenario and then locates the relevant argparser.Command struct, passing it to the 'CommandHook'. Example implementations for two test scenarios for 'fastly compute acl create' are included; one example demonstrates testing the content of the input structure passed to the mock function.

kpfleming · 2026-03-19T19:12:18Z

The implementation of this has changed substantially so I'm going to open a new PR with the cleaned-up branch, which will also have more documentation.

kpfleming added DO NOT MERGE YET Skip-Changelog do not add a changelog entry for this change labels Mar 11, 2026

kpfleming force-pushed the go-fastly-api-mocks branch 3 times, most recently from df49875 to 5b750d9 Compare March 12, 2026 15:09