metropolis/pkg/supervisor/supervisor_testhelpers.go

// Copyright 2020 The Monogon Project Authors.
//
// SPDX-License-Identifier: Apache-2.0
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package supervisor

import (
	"context"
	"errors"
	"testing"

	"source.monogon.dev/metropolis/pkg/logtree"
)

// TestHarness runs a supervisor in a harness designed for unit testing
// runnables and runnable trees.
//
// The given runnable will be run in a new supervisor, and the logs from this
// supervisor will be streamed to stderr. If the runnable returns a non-context
// error, the harness will throw a test error, but will not abort the test.
//
// The harness also returns a context cancel function that can be used to
// terminate the started supervisor early.  Regardless of manual cancellation,
// the supervisor will always be terminated up at the end of the test/benchmark
// it's running in.
//
// The second returned value is the logtree used by this supervisor. It can be
// used to assert some log messages are emitted in tests that exercise some
// log-related functionality.
func TestHarness(t *testing.T, r func(ctx context.Context) error) (context.CancelFunc, *logtree.LogTree) {
	t.Helper()

	ctx, ctxC := context.WithCancel(context.Background())
	t.Cleanup(ctxC)

	lt := logtree.New()
	logtree.PipeAllToStderr(t, lt)

	New(ctx, func(ctx context.Context) error {
		if err := r(ctx); err != nil && !errors.Is(err, ctx.Err()) {
			t.Errorf("Supervised runnable in harness returned error: %v", err)
		}
		return nil
	}, WithExistingLogtree(lt))
	return ctxC, lt
}