lib/file: add tests for WriteAtomic

lib/file/atomic_test.go

@@ -0,0 +1,32 @@
+package file
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+// This doesn't really test the "atomic" part of this function. It really
+// tests that it just writes the file properly. I would love to test this
+// better but I'm not sure how. -mitchellh
+func TestWriteAtomic(t *testing.T) {
+	require := require.New(t)
+	td, err := ioutil.TempDir("", "lib-file")
+	require.NoError(err)
+	defer os.RemoveAll(td)
+
+	// Create a subdir that doesn't exist to test that it is created
+	path := filepath.Join(td, "subdir", "file")
+
+	// Write
+	expected := []byte("hello")
+	require.NoError(WriteAtomic(path, expected))
+
+	// Read and verify
+	actual, err := ioutil.ReadFile(path)
+	require.NoError(err)
+	require.Equal(expected, actual)
+}