RTCP: Add util/GetPadding

Simple helper function to do 32bit padding calculation

Relates to #119

internal/util/util_test.go

@@ -0,0 +1,40 @@
+package util
+
+import (
+	"regexp"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRandSeq(t *testing.T) {
+	if len(RandSeq(10)) != 10 {
+		t.Errorf("RandSeq return invalid length")
+	}
+
+	var isLetter = regexp.MustCompile(`^[a-zA-Z]+$`).MatchString
+	if !isLetter(RandSeq(10)) {
+		t.Errorf("RandSeq should be AlphaNumeric only")
+	}
+}
+
+func TestGetPadding(t *testing.T) {
+	assert := assert.New(t)
+	type testCase struct {
+		input  int
+		result int
+	}
+
+	cases := []testCase{
+		{input: 0, result: 0},
+		{input: 1, result: 3},
+		{input: 2, result: 2},
+		{input: 3, result: 1},
+		{input: 4, result: 0},
+		{input: 100, result: 0},
+		{input: 500, result: 0},
+	}
+	for _, testCase := range cases {
+		assert.Equalf(GetPadding(testCase.input), testCase.result, "Test case returned wrong value for input %d", testCase.input)
+	}
+}