Render templates via a buffer, not the ResponseWriter (closes #123)

internal/handlers/export_test.go

@@ -1,6 +1,19 @@
 package handlers
 
-import "net/http"
+import (
+	"html/template"
+	"net/http"
+)
+
+// AddTemplateForTest registers a template under a page name so that
+// the handlers_test package can drive the render path with a
+// template of its own.
+func (s *Handlers) AddTemplateForTest(
+	pageTemplate string,
+	tmpl *template.Template,
+) {
+	s.templates[pageTemplate] = tmpl
+}
 
 // RenderTemplateForTest exposes renderTemplate for use in the
 // handlers_test package.