Add test for variable declaration

testing/templates/let-decl.html

@@ -0,0 +1,7 @@
+{% let val -%}
+{% if cond -%}
+  {% let val = "foo" -%}
+{% else -%}
+  {% let val = s -%}
+{% endif -%}
+{{ val }}

testing/tests/vars.rs

@@ -14,3 +14,17 @@ fn test_let() {
     let t = LetTemplate { s: "foo" };
     assert_eq!(t.render().unwrap(), "foo");
 }
+
+
+#[derive(Template)]
+#[template(path = "let-decl.html")]
+struct LetDeclTemplate<'a> {
+    cond: bool,
+    s: &'a str,
+}
+
+#[test]
+fn test_let_decl() {
+    let t = LetDeclTemplate { cond: false, s: "bar" };
+    assert_eq!(t.render().unwrap(), "bar");
+}