Add lib/diskusage to measure used/free on disks

lib/diskusage/diskusage_test.go

@@ -0,0 +1,23 @@
+package diskusage
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNew(t *testing.T) {
+	info, err := New(".")
+	if err == ErrUnsupported {
+		t.Skip(err)
+	}
+	require.NoError(t, err)
+	t.Logf("Free      %16d", info.Free)
+	t.Logf("Available %16d", info.Available)
+	t.Logf("Total     %16d", info.Total)
+	assert.True(t, info.Total != 0)
+	assert.True(t, info.Total > info.Free)
+	assert.True(t, info.Total > info.Available)
+	assert.True(t, info.Free >= info.Available)
+}