Add corner cases.

module/cornercases_test.go

@@ -0,0 +1,48 @@
+package module
+
+import (
+	"context"
+	"testing"
+)
+
+func TestProviderReturnNilInterfaceWithoutError(t *testing.T) {
+	type Interface interface{}
+	newNilInterface := func(context.Context) (Interface, error) {
+		return nil, nil
+	}
+	moduleInterface := New(newNilInterface)
+
+	repo := NewRepo()
+	repo.AddModule(moduleInterface)
+
+	ctx, err := repo.InjectTo(context.Background())
+	if err != nil {
+		t.Fatal("inject error:", err)
+	}
+
+	var got Interface = moduleInterface.Value(ctx)
+	if got != nil {
+		t.Errorf("moduleInterface.Value(ctx) = %v, want: nil", got)
+	}
+}
+
+func TestProviderReturnNilPointerWithoutError(t *testing.T) {
+	type Instance struct{}
+	newNilInstance := func(context.Context) (*Instance, error) {
+		return nil, nil
+	}
+	moduleInstance := New(newNilInstance)
+
+	repo := NewRepo()
+	repo.AddModule(moduleInstance)
+
+	ctx, err := repo.InjectTo(context.Background())
+	if err != nil {
+		t.Fatal("inject error:", err)
+	}
+
+	var got *Instance = moduleInstance.Value(ctx)
+	if got != nil {
+		t.Errorf("moduleInstance.Value(ctx) = %v, want: nil", got)
+	}
+}