Add internal randstream and pwgen packages

internal/randstream/randstream_test.go

@@ -0,0 +1,111 @@
+package randstream_test
+
+import (
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"sneak.berlin/go/x/internal/randstream"
+)
+
+const (
+	sampleSize = 1 << 20
+	helloSeed  = "hello"
+)
+
+func TestSeededStreamIsDeterministic(t *testing.T) {
+	t.Parallel()
+
+	first := readSample(t, randstream.Params{Seed: helloSeed}, sampleSize)
+	second := readSample(t, randstream.Params{Seed: helloSeed}, sampleSize)
+
+	assert.Equal(t, first, second)
+}
+
+func TestDifferentSeedsDiffer(t *testing.T) {
+	t.Parallel()
+
+	hello := readSample(t, randstream.Params{Seed: helloSeed}, sampleSize)
+	world := readSample(t, randstream.Params{Seed: "world"}, sampleSize)
+
+	assert.NotEqual(t, hello, world)
+}
+
+func TestUnseededStreamsDiffer(t *testing.T) {
+	t.Parallel()
+
+	first := readSample(t, randstream.Params{Seed: ""}, sampleSize)
+	second := readSample(t, randstream.Params{Seed: ""}, sampleSize)
+
+	assert.NotEqual(t, first, second)
+}
+
+func TestReadAlwaysFillsBuffer(t *testing.T) {
+	t.Parallel()
+
+	stream, err := randstream.New(randstream.Params{Seed: "fill"})
+	require.NoError(t, err)
+
+	for _, size := range []int{0, 1, 7, 64, 65, 4096, sampleSize} {
+		buffer := make([]byte, size)
+
+		n, err := stream.Read(buffer)
+		require.NoError(t, err)
+		assert.Equal(t, size, n)
+	}
+}
+
+func TestStreamIsContinuousAcrossReads(t *testing.T) {
+	t.Parallel()
+
+	const headSize, tailSize = 300, 700
+
+	whole := readSample(t, randstream.Params{Seed: "continuous"}, headSize+tailSize)
+
+	stream, err := randstream.New(randstream.Params{Seed: "continuous"})
+	require.NoError(t, err)
+
+	head := make([]byte, headSize)
+	tail := make([]byte, tailSize)
+
+	_, err = io.ReadFull(stream, head)
+	require.NoError(t, err)
+
+	_, err = io.ReadFull(stream, tail)
+	require.NoError(t, err)
+
+	assert.Equal(t, whole[:headSize], head)
+	assert.Equal(t, whole[headSize:], tail)
+}
+
+func TestOutputIsNotTriviallyPatterned(t *testing.T) {
+	t.Parallel()
+
+	sample := readSample(t, randstream.Params{Seed: "entropy"}, sampleSize)
+
+	var seen [256]bool
+	for _, b := range sample {
+		seen[b] = true
+	}
+
+	for value, wasSeen := range seen {
+		assert.True(t, wasSeen, "byte value %d never appeared", value)
+	}
+}
+
+// readSample reads size bytes from a new Reader configured by p.
+func readSample(t *testing.T, p randstream.Params, size int) []byte {
+	t.Helper()
+
+	stream, err := randstream.New(p)
+	require.NoError(t, err)
+
+	sample := make([]byte, size)
+
+	_, err = io.ReadFull(stream, sample)
+	require.NoError(t, err)
+
+	return sample
+}