Add test for == operator

testing/templates/eq.html

@@ -0,0 +1 @@
+{% if a == b %}t{% endif %}{% if a == c %}t{% else %}f{% endif %}

testing/tests/comparison.rs

@@ -0,0 +1,19 @@
+extern crate askama;
+#[macro_use]
+extern crate askama_derive;
+
+use askama::Template;
+
+#[derive(Template)]
+#[template(path = "eq.html")]
+struct EqTemplate {
+    a: usize,
+    b: usize,
+    c: usize,
+}
+
+#[test]
+fn test_eq() {
+    let t = EqTemplate { a: 1, b: 1, c: 2 };
+    assert_eq!(t.render(), "tf\n");
+}