Add tests for filter

sailfish-tests/integration-tests/templates/filter.out

@@ -0,0 +1,4 @@
+disp: hello
+dbg: "hello"
+disp escaped: hello
+dbg escaped: "hello"

sailfish-tests/integration-tests/templates/filter.stpl

@@ -0,0 +1,4 @@
+disp: <%- message | disp %>
+dbg: <%- message | dbg %>
+disp escaped: <%= message | disp %>
+dbg escaped: <%= message | dbg %>

sailfish-tests/integration-tests/templates/json.stpl

@@ -1,4 +1,4 @@
 {
-    "name": "<%= name %>",
+    "name": <%- name | dbg %>,
     "value": <%= value %>
 }

sailfish-tests/integration-tests/tests/template_once.rs

@@ -200,6 +200,17 @@ fn test_formatting() {
     assert_render("formatting", Formatting);
 }
 
+#[derive(TemplateOnce)]
+#[template(path = "filter.stpl")]
+struct Filter<'a> {
+    message: &'a str,
+}
+
+#[test]
+fn test_filter() {
+    assert_render("filter", Filter { message: "hello" });
+}
+
 #[cfg(unix)]
 mod unix {
     use super::*;

sailfish/src/runtime/filter.rs

@@ -85,3 +85,23 @@ impl<'a, T: Render> Render for Lower<'a, T> {
 pub fn lower<T: Render>(expr: &T) -> Lower<T> {
     Lower(expr)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn case() {
+        let mut buf = Buffer::new();
+        upper(&"hElLO, WOrLd!").render(&mut buf).unwrap();
+        assert_eq!(buf.as_str(), "HELLO, WORLD!");
+
+        buf.clear();
+        lower(&"hElLO, WOrLd!").render(&mut buf).unwrap();
+        assert_eq!(buf.as_str(), "hello, world!");
+
+        buf.clear();
+        lower(&"<h1>TITLE</h1>").render_escaped(&mut buf).unwrap();
+        assert_eq!(buf.as_str(), "&lt;h1&gt;title&lt;/h1&gt;");
+    }
+}