Validate Slack target URLs at creation time (closes #68)

internal/handlers/export_test.go

@@ -12,3 +12,13 @@ func (s *Handlers) RenderTemplateForTest(
 ) {
 	s.renderTemplate(w, r, pageTemplate, data)
 }
+
+// BuildSlackTargetConfigForTest exposes buildSlackTargetConfig
+// for use in the handlers_test package.
+func (s *Handlers) BuildSlackTargetConfigForTest(
+	w http.ResponseWriter,
+	r *http.Request,
+	targetURL string,
+) (string, error) {
+	return s.buildSlackTargetConfig(w, r, targetURL)
+}