diff --git a/src/iact_estimator/tests/__init__.py b/src/iact_estimator/tests/__init__.py
new file mode 100644
index 0000000..5a68c2b
--- /dev/null
+++ b/src/iact_estimator/tests/__init__.py
@@ -0,0 +1 @@
+"""Testing suite for iact-estimator."""
diff --git a/src/iact_estimator/tests/test_io.py b/src/iact_estimator/tests/test_io.py
new file mode 100644
index 0000000..789affa
--- /dev/null
+++ b/src/iact_estimator/tests/test_io.py
@@ -0,0 +1,18 @@
+def test_read_yaml(tmp_path):
+    from ..io import read_yaml
+
+    test_file = tmp_path / "test_file.yml"
+    test_file.write_text(
+        """
+        a: 1
+        b:
+            c: 3
+            d: 4
+        """
+    )
+
+    data = read_yaml(test_file)
+
+    assert data["a"] == 1
+    assert data["b"]["c"] == 3
+    assert data["b"]["d"] == 4
diff --git a/src/iact_estimator/tests/test_spectral.py b/src/iact_estimator/tests/test_spectral.py
new file mode 100644
index 0000000..0905ad2
--- /dev/null
+++ b/src/iact_estimator/tests/test_spectral.py
@@ -0,0 +1,24 @@
+# Test cases automatically generated by Pynguin (https://www.pynguin.eu).
+# Please check them before you use them.
+
+import astropy.units as u
+import numpy as np
+
+
+def test_crab_nebula_spectrum():
+    from ..spectral import crab_nebula_spectrum
+
+    spectrum = crab_nebula_spectrum()
+
+    assert spectrum.amplitude.unit == u.Unit("TeV^-1 s^-1 cm^-2")
+    assert spectrum.reference.unit == u.TeV
+
+    assert np.allclose(
+        [
+            spectrum.alpha.value,
+            spectrum.beta.value,
+            spectrum.amplitude.value,
+            spectrum.reference.value,
+        ],
+        [2.51, 0.21 / np.log(10), 3.39e-11, 1.0],
+    )