How to make the function suit the _test file?

Here was my code

type Queue interface {
	Push(key interface{})
	Pop() interface{}
	Contains(key interface{}) bool
	Len() int
	Keys() []interface{}
}

type QueueData struct {
	size int
	data []interface{}
}

func New(size int) *QueueData {
	return &QueueData{
		size: size,
	}
}

func (q *QueueData) IsEmpty() bool {
	return len(q.data) == 0
}

// Peek : returns the next element in the queue
func (q *QueueData) Peek() (interface{}, error) {
	if len(q.data) == 0 {
		return 0, fmt.Errorf("Queue is empty")
	}
	return q.data[0], nil
}

// Queue : adds an element onto the queue and returns an pointer to the current queue
func (q *QueueData) Push(n interface{}) *QueueData {
	if q.Len() < q.size {
		q.data = append(q.data, n)
	} else {
		q.Pop()
		q.Push(n)
	}
	return q
}

// Dequeue : removes the next element from the queue and returns its value
//func (q *QueueFix) Pop() (interface{}, error) {
func (q *QueueData) Pop() interface{} {
	if len(q.data) == 0 {
		//return 0, fmt.Errorf("Queue is empty")
		return 0
	}
	element := q.data[0]
	q.data = q.data[1:]
	//return element, nil
	return element
}

func (q *QueueData) Len() int {
	return len(q.data)
}

func (q *QueueData) Keys() []interface{} {
	return q.data
}

func (q *QueueData) Contains(key interface{}) bool {
	cont := false
	for i := 0; i < q.Len(); i++ {
		if q.data[i] == key {
			cont = true
		}
	}
	return cont
}

My Test is look like this...

var testValues = []interface{}{
	"lorem",
	"ipsum",
	1,
	2,
	3,
	"jack",
	"jill",
	"felix",
	"donking",
}

// TestPush validate evict old item policy
func TestEvictPolicy(t *testing.T) {
	size := 5
	q := New(size)

	for i, v := range testValues {
		q.Push(v)

		t.Log("current: ", q.Keys())

		// validate
		// item existence
		if !q.Contains(v) {
			t.Errorf("policy: newly inserted %v must be exists", v)
		}

		if i < 5 && q.Len() != (i+1) {
			t.Errorf("expected length %d but actual: %d", i+1, q.Len())
		} else if i >= 5 && q.Len() != 5 {
			t.Errorf("expexted length: %d but actual: %d", size, q.Len())
		}
	}
}

// TestPop validate pop item policy
func TestPop(t *testing.T) {
	size := 5
	q := New(size)

	for _, v := range testValues {
		q.Push(v)
	}

	for q.Len() > 0 {
		t.Log("current: ", q.Keys())

		v := q.Pop()

		// validate
		expect := testValues[len(testValues)-(q.Len()+1)]
		if v != expect {
			t.Error("expected %v but recevied %v", expect, v)
		}
	}

}

The test returned

> .\Queue_test.go:60:4: Error call has possible formatting directive %v
> FAIL /C/Users/richa/go/src [build failed]

I didn't i understand how to make an code from _test.go file. Need an explain how to make the _test.go aswell. Just give some reference for this testing. like when i add EvictPolicy Function, itsay undeclared...

The error you are seeing

Queue_test.go:60:4: Error call has possible formatting directive %v FAIL

Looks to be referring to this line

t.Error("expected %v but recevied %v", expect, v)

On this line you called t.Error to print the error message and format the expect and v vars into the error string. But, t.Error does not format the additional arguments. It just prints them.

You should call t.Errorf like you did for your other error messages.