first commit

README.md

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+# omg.testingTools
+
+---
+

go.mod

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+module omg.testingtools
+
+go 1.17

setPrivateValue.go

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+package testingtools
+
+import (
+	"fmt"
+	"reflect"
+	"unsafe"
+)
+
+func SetPrivateValue(obj interface{}, fieldName string, value interface{}) {
+	reflectValue := reflect.ValueOf(obj)
+
+	if reflectValue.Kind() != reflect.Ptr {
+		panic("object is not a pointer")
+	}
+
+	reflectValue = reflectValue.Elem()
+	reflectType := reflect.TypeOf(obj).Elem()
+
+	if reflectValue.Kind() != reflect.Struct {
+		panic("object is not a pointer to struct")
+	}
+
+	newReflectValueType := reflect.TypeOf(value)
+
+	var offset uintptr
+
+	for i := 0; i < reflectValue.NumField(); i++ {
+		if reflectType.Field(i).Name == fieldName {
+			currentFieldType := reflectType.Field(i).Type.String()
+
+			if newReflectValueType.String() != currentFieldType {
+				panic(fmt.Sprintf("incorrect type: must be %s", currentFieldType))
+			}
+
+			fieldPtr := unsafe.Pointer(reflectValue.UnsafeAddr() + offset)
+			reflect.NewAt(newReflectValueType, fieldPtr).Elem().Set(reflect.ValueOf(value))
+
+			return
+		}
+
+		offset += reflectValue.Field(i).Type().Size()
+	}
+
+	panic(fmt.Sprintf("Field [%s] not found in struct", fieldName))
+}

setPrivateValue_test.go

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+package testingtools
+
+import (
+	"fmt"
+	"omg.testingtools/testmodule"
+	"testing"
+)
+
+func TestSetPrivateValue(t *testing.T) {
+	qq := testmodule.NewQQ(123, "abc", []int{5, 6, 7})
+
+	SetPrivateValue(&qq, "c", []int{1, 2, 3, 4})
+	SetPrivateValue(&qq, "b", "qwe")
+
+	if fmt.Sprint(qq) != "{123 qwe [1 2 3 4]}" {
+		t.Fail()
+	}
+}

testmodule/omg.go

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+package testmodule
+
+type TestStruct struct {
+	a int
+	b string
+	c []int
+}
+
+func NewQQ(a int, b string, c []int) TestStruct {
+	return TestStruct{
+		a, b, c,
+	}
+}