diff --git a/test/test_texenv.py b/test/test_texenv.py
index dc0d353..e68c5b4 100644
--- a/test/test_texenv.py
+++ b/test/test_texenv.py
@@ -29,3 +29,12 @@ def test_block_line_statement_with_comment():
     jinja2_template = texenv.from_string(base_template)
     output = jinja2_template.render()
     assert output == "\n2"
+
+def test_add_filter():
+    texenv.filters["count_caracters"] = lambda x: len(x)
+    base_template = r"""\Var{a} has \Var{a | count_caracters}"""
+    jinja2_template = texenv.from_string(base_template)
+    output = jinja2_template.render(a="coucou")
+    assert output == "coucou has 6"
+    
+