go-process/buffer_test.go

package process

import (
	"sync"
	"testing"

	"github.com/stretchr/testify/assert"
)

func TestBuffer_Write_Good(t *testing.T) {
	t.Run("write and read", func(t *testing.T) {
		rb := NewRingBuffer(10)

		itemCount, err := rb.Write([]byte("hello"))
		assert.NoError(t, err)
		assert.Equal(t, 5, itemCount)
		assert.Equal(t, "hello", rb.String())
		assert.Equal(t, 5, rb.Len())
	})

	t.Run("overflow wraps around", func(t *testing.T) {
		rb := NewRingBuffer(5)

		_, _ = rb.Write([]byte("hello"))
		assert.Equal(t, "hello", rb.String())

		_, _ = rb.Write([]byte("world"))
		// Should contain "world" (overwrote "hello")
		assert.Equal(t, 5, rb.Len())
		assert.Equal(t, "world", rb.String())
	})

	t.Run("partial overflow", func(t *testing.T) {
		rb := NewRingBuffer(10)

		_, _ = rb.Write([]byte("hello"))
		_, _ = rb.Write([]byte("worldx"))
		// Should contain "lloworldx" (11 chars, buffer is 10)
		assert.Equal(t, 10, rb.Len())
	})

	t.Run("bytes returns copy", func(t *testing.T) {
		rb := NewRingBuffer(10)
		_, _ = rb.Write([]byte("hello"))

		contents := rb.Bytes()
		assert.Equal(t, []byte("hello"), contents)

		// Modifying returned bytes shouldn't affect buffer
		contents[0] = 'x'
		assert.Equal(t, "hello", rb.String())
	})
}

func TestBuffer_Write_Bad(t *testing.T) {
	t.Run("empty write is a no-op", func(t *testing.T) {
		rb := NewRingBuffer(10)
		itemCount, err := rb.Write([]byte{})
		assert.NoError(t, err)
		assert.Equal(t, 0, itemCount)
		assert.Equal(t, "", rb.String())
	})
}

func TestBuffer_Write_Ugly(t *testing.T) {
	t.Run("concurrent writes do not race", func(t *testing.T) {
		rb := NewRingBuffer(64)
		var wg sync.WaitGroup
		for i := 0; i < 10; i++ {
			wg.Add(1)
			go func() {
				defer wg.Done()
				_, _ = rb.Write([]byte("data"))
			}()
		}
		wg.Wait()
		// Buffer should not panic and length should be bounded by capacity
		assert.LessOrEqual(t, rb.Len(), rb.Cap())
	})
}

func TestBuffer_String_Good(t *testing.T) {
	t.Run("empty buffer returns empty string", func(t *testing.T) {
		rb := NewRingBuffer(10)
		assert.Equal(t, "", rb.String())
	})

	t.Run("full buffer wraps correctly", func(t *testing.T) {
		rb := NewRingBuffer(5)
		_, _ = rb.Write([]byte("abcde"))
		assert.Equal(t, "abcde", rb.String())
	})
}

func TestBuffer_String_Bad(t *testing.T) {
	t.Run("overflowed buffer reflects newest data", func(t *testing.T) {
		rb := NewRingBuffer(5)
		_, _ = rb.Write([]byte("hello"))
		_, _ = rb.Write([]byte("world"))
		// Oldest bytes ("hello") have been overwritten
		assert.Equal(t, "world", rb.String())
	})
}

func TestBuffer_String_Ugly(t *testing.T) {
	t.Run("size-1 buffer holds only last byte", func(t *testing.T) {
		rb := NewRingBuffer(1)
		_, _ = rb.Write([]byte("abc"))
		assert.Equal(t, "c", rb.String())
	})
}

func TestBuffer_Reset_Good(t *testing.T) {
	t.Run("clears all data", func(t *testing.T) {
		rb := NewRingBuffer(10)
		_, _ = rb.Write([]byte("hello"))
		rb.Reset()
		assert.Equal(t, "", rb.String())
		assert.Equal(t, 0, rb.Len())
	})

	t.Run("cap returns buffer capacity", func(t *testing.T) {
		rb := NewRingBuffer(42)
		assert.Equal(t, 42, rb.Cap())
	})
}

func TestBuffer_Reset_Bad(t *testing.T) {
	t.Run("reset on empty buffer is a no-op", func(t *testing.T) {
		rb := NewRingBuffer(10)
		rb.Reset()
		assert.Equal(t, "", rb.String())
		assert.Equal(t, 0, rb.Len())
	})
}

func TestBuffer_Reset_Ugly(t *testing.T) {
	t.Run("reset after overflow allows fresh writes", func(t *testing.T) {
		rb := NewRingBuffer(5)
		_, _ = rb.Write([]byte("hello"))
		_, _ = rb.Write([]byte("world"))
		rb.Reset()
		_, _ = rb.Write([]byte("new"))
		assert.Equal(t, "new", rb.String())
	})
}