Introduce a Promise typeHEADmain

1 files changed, 89 insertions, 0 deletions

diff --git a/promise_test.go b/promise_test.go
new file mode 100644
index 0000000..bafa184
--- /dev/null
+++ b/promise_test.go
@@ -0,0 +1,89 @@
+// SPDX-FileCopyrightText: © 2024 Grégoire Duchêne <gduchene@awhk.org>
+// SPDX-License-Identifier: ISC
+
+package core_test
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"testing"
+	"time"
+
+	"go.awhk.org/core"
+)
+
+func TestPromise(s *testing.T) {
+	t := core.T{T: s}
+	someError := errors.New("some error")
+
+	t.Run("Success", func(t *core.T) {
+		p := core.NewPromise[int]()
+
+		t.AssertErrorIs(nil, p.SucceedWith(1))
+		t.AssertEqual(1, <-p.Value())
+	})
+
+	t.Run("SuccessThenError", func(t *core.T) {
+		p := core.NewPromise[int]()
+
+		t.AssertErrorIs(nil, p.SucceedWith(1))
+		t.AssertErrorIs(core.ErrPromiseFulfilled, p.FailWith(someError))
+		t.AssertEqual(1, <-p.Value())
+	})
+
+	t.Run("Error", func(t *core.T) {
+		p := core.NewPromise[int]()
+
+		t.AssertErrorIs(nil, p.FailWith(someError))
+		t.AssertErrorIs(someError, <-p.Err())
+	})
+
+	t.Run("ErrorThenSuccess", func(t *core.T) {
+		p := core.NewPromise[int]()
+
+		t.AssertErrorIs(nil, p.FailWith(someError))
+		t.AssertErrorIs(core.ErrPromiseFulfilled, p.SucceedWith(1))
+		t.AssertErrorIs(someError, <-p.Err())
+	})
+}
+
+func ExamplePromise() {
+	p := core.NewPromise[string]()
+
+	go func() {
+		time.Sleep(time.Millisecond)
+		p.SucceedWith("Hello World!")
+	}()
+
+	select {
+	case s := <-p.Value():
+		fmt.Printf("Received %q.\n", s)
+	case err := <-p.Err():
+		fmt.Printf("Received an error: %s.\n", err)
+	}
+	// Output: Received "Hello World!".
+}
+
+func ExamplePromise_withContext() {
+	var (
+		ctx, cancel = context.WithTimeout(context.Background(), time.Second)
+		p           = core.NewPromise[string]()
+	)
+	defer cancel()
+
+	go func() {
+		time.Sleep(time.Millisecond)
+		p.FailWith(errors.New("some error"))
+	}()
+
+	select {
+	case s := <-p.Value():
+		fmt.Printf("Received %q.\n", s)
+	case err := <-p.Err():
+		fmt.Printf("Received an error: %s.\n", err)
+	case <-ctx.Done():
+		fmt.Printf("Context was cancelled: %s.\n", ctx.Err())
+	}
+	// Output: Received an error: some error.
+}