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Before synctest, timers was needed to allow the events to flow into the test bus. There is still a timer, but this one is not derived from the test deadline and it is mostly arbitrary as synctest will render it practically non-existent. With this approach, tests that do not need to test for the absence of events do not rely on synctest. Updates #15160 Signed-off-by: Claus Lensbøl <claus@tailscale.com>
60 lines
2.3 KiB
Go
60 lines
2.3 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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// Package eventbustest provides helper methods for testing an [eventbus.Bus].
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//
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// # Usage
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//
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// A [Watcher] presents a set of generic helpers for testing events.
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//
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// To test code that generates events, create a [Watcher] from the [eventbus.Bus]
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// used by the code under test, run the code to generate events, then use the watcher
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// to verify that the expected events were produced. In outline:
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//
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// bus := eventbustest.NewBus(t)
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// tw := eventbustest.NewWatcher(t, bus)
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// somethingThatEmitsSomeEvent()
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// if err := eventbustest.Expect(tw, eventbustest.Type[EventFoo]()); err != nil {
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// t.Error(err.Error())
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// }
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//
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// As shown, [Expect] checks that at least one event of the given type occurs
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// in the stream generated by the code under test.
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//
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// The following functions all take an any parameter representing a function.
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// This function will take an argument of the expected type and is used to test
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// for the events on the eventbus being of the given type. The function can
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// take the shape described in [Expect].
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//
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// [Type] is a helper for only testing event type.
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//
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// To check for specific properties of an event, use [Expect], and pass a function
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// as the second argument that tests for those properties.
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//
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// To test for multiple events, use [Expect], which checks that the stream
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// contains the given events in the given order, possibly with other events
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// interspersed.
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//
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// To test the complete contents of the stream, use [ExpectExactly], which
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// checks that the stream contains exactly the given events in the given order,
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// and no others.
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//
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// To test for the absence of events, use [ExpectExactly] without any
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// expected events, along side [testing/synctest] to avoid waiting for timers
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// to ensure that no events are produced. This will look like:
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//
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// synctest.Test(t, func(t *testing.T) {
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// bus := eventbustest.NewBus(t)
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// tw := eventbustest.NewWatcher(t, bus)
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// somethingThatShouldNotEmitsSomeEvent()
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// synctest.Wait()
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// if err := eventbustest.ExpectExactly(tw); err != nil {
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// t.Errorf("Expected no events or errors, got %v", err)
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// }
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// })
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//
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// See the [usage examples].
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//
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// [usage examples]: https://github.com/tailscale/tailscale/blob/main/util/eventbus/eventbustest/examples_test.go
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package eventbustest
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