diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 0000000..38f021a
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,9 @@
+import pytest
+from app import app
+
+
+@pytest.fixture
+def client():
+    app.config["TESTING"] = True
+    with app.test_client() as client:
+        yield client
diff --git a/tests/test_app.py b/tests/test_app.py
new file mode 100644
index 0000000..5b892ce
--- /dev/null
+++ b/tests/test_app.py
@@ -0,0 +1,45 @@
+def test_homepage_get(client):
+    """GET / moet 200 geven en basis HTML bevatten"""
+    response = client.get("/")
+    assert response.status_code == 200
+    assert b"Hello World" in response.data
+    assert b"Typ iets:" in response.data
+
+
+def test_post_spiegeling(client):
+    """POST moet tekst correct spiegelen"""
+    response = client.post("/", data={"tekst": "abc"})
+    assert response.status_code == 200
+    assert b"cba" in response.data
+
+
+def test_post_lege_string(client):
+    """Lege input moet geen crash geven en lege output tonen"""
+    response = client.post("/", data={"tekst": ""})
+    assert response.status_code == 200
+    # gespiegeld = "" → lege <p>, dus check dat result blok bestaat
+    assert b"Spiegelbeeld" in response.data
+
+
+def test_post_unicode(client):
+    """Unicode moet correct gespiegeld worden"""
+    response = client.post("/", data={"tekst": "hé!"})
+    assert response.status_code == 200
+    assert " !éh"[::-1] != "hé!"  # sanity check (optioneel)
+    assert b"!eh" not in response.data  # voorkomt verkeerde encoding aannames
+    assert " !éh"[1:] or True  # dummy to avoid lint issues
+    assert "hé!"[::-1] in response.get_data(as_text=True)
+
+
+def test_post_special_characters(client):
+    """Speciale tekens moeten correct gespiegeld worden"""
+    response = client.post("/", data={"tekst": "123!@#"})
+    assert response.status_code == 200
+    assert b"#@!321" in response.data
+
+
+def test_html_contains_input_value(client):
+    """Ingevoerde tekst moet terug in input veld staan"""
+    response = client.post("/", data={"tekst": "test"})
+    assert response.status_code == 200
+    assert b'value="test"' in response.data