add commands support

Signed-off-by: Casey Lee <cplee@nektos.com>

pkg/common/line_writer_test.go

@@ -0,0 +1,36 @@
+package common
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestLineWriter(t *testing.T) {
+	lines := make([]string, 0)
+	lineHandler := func(s string) {
+		lines = append(lines, s)
+	}
+
+	lineWriter := NewLineWriter(lineHandler)
+
+	assert := assert.New(t)
+	write := func(s string) {
+		n, err := lineWriter.Write([]byte(s))
+		assert.NoError(err)
+		assert.Equal(len(s), n, s)
+	}
+
+	write("hello")
+	write(" ")
+	write("world!!\nextra")
+	write(" line\n and another\nlast")
+	write(" line\n")
+	write("no newline here...")
+
+	assert.Len(lines, 4)
+	assert.Equal("hello world!!\n", lines[0])
+	assert.Equal("extra line\n", lines[1])
+	assert.Equal(" and another\n", lines[2])
+	assert.Equal("last line\n", lines[3])
+}