Fs (#242)

* play around with fs idea

* docs and fix test

* better docs

middleware/fs_test.go

@@ -0,0 +1,19 @@
+package middleware
+
+import (
+	"os"
+	"strings"
+	"testing"
+)
+
+func TestfsPath(t *testing.T) {
+	if actual := fsPath(); !strings.HasSuffix(actual, ".coredns") {
+		t.Errorf("Expected path to be a .coredns folder, got: %v", actual)
+	}
+
+	os.Setenv("COREDNSPATH", "testpath")
+	defer os.Setenv("COREDNSPATH", "")
+	if actual, expected := fsPath(), "testpath"; actual != expected {
+		t.Errorf("Expected path to be %v, got: %v", expected, actual)
+	}
+}