tests: add locker and math tests

pkg/locker/locker.go

@@ -25,4 +25,17 @@ func (s *Locked[T]) Modify(ctx context.Context, fn func(*T) error) error {
 	case <-ctx.Done():
 		return ctx.Err()
 	}
-}
+}
+
+func (s *Locked[T]) Copy(ctx context.Context) (T, error) {
+	var t T
+
+	err := s.Modify(ctx, func(c *T) error {
+		if c != nil {
+			t = *c
+		}
+		return nil
+	})
+
+	return t, err
+}

pkg/locker/locker_test.go

@@ -0,0 +1,62 @@
+package locker_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/matryer/is"
+
+	"github.com/sour-is/ev/pkg/locker"
+)
+
+type config struct {
+	Value   string
+	Counter int
+}
+
+func TestLocker(t *testing.T) {
+	is := is.New(t)
+
+	value := locker.New(&config{})
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	err := value.Modify(ctx, func(c *config) error {
+		c.Value = "one"
+		c.Counter++
+		return nil
+	})
+	is.NoErr(err)
+
+	c, err := value.Copy(context.Background())
+
+	is.NoErr(err)
+	is.Equal(c.Value, "one")
+	is.Equal(c.Counter, 1)
+
+	wait := make(chan struct{})
+
+	go value.Modify(ctx, func(c *config) error {
+		c.Value = "two"
+		c.Counter++
+		close(wait)
+		return nil
+	})
+
+	<-wait
+	cancel()
+
+	err = value.Modify(ctx, func(c *config) error {
+		c.Value = "three"
+		c.Counter++
+		return nil
+	})
+	is.True(err != nil)
+
+	c, err = value.Copy(context.Background())
+
+	is.NoErr(err)
+	is.Equal(c.Value, "two")
+	is.Equal(c.Counter, 2)
+}