diff --git a/src/scgenerator/legacy.py b/src/scgenerator/legacy.py
index ac02a7a..c812edd 100644
--- a/src/scgenerator/legacy.py
+++ b/src/scgenerator/legacy.py
@@ -1,6 +1,6 @@
 import os
 import sys
-from collections import MutableMapping
+from collections.abc import MutableMapping
 from pathlib import Path
 from typing import Any, Set
 
@@ -93,13 +93,18 @@ def translate_parameters(d: dict[str, Any]) -> dict[str, Any]:
     Parameters
     ----------
     d : dict[str, Any]
-        [description]
+        any parameter dictionary WITHOUT "variable" part
 
     Returns
     -------
     dict[str, Any]
-        [description]
+        translated parameters
     """
+    if {"variable", "Fiber"} & d.keys():
+        raise ValueError(
+            "The dict to translate should be a single parameter set "
+            "(no 'variable' nor 'Fiber' entry)"
+        )
     old_names = dict(
         interp_degree="interpolation_degree",
         beta="beta2_coefficients",
diff --git a/src/scgenerator/math.py b/src/scgenerator/math.py
index 0037f2a..68c0968 100644
--- a/src/scgenerator/math.py
+++ b/src/scgenerator/math.py
@@ -65,6 +65,7 @@ def _power_fact_single(x, n):
 
 
 def _power_fact_array(x, n):
+    """returns x^2/n!"""
     result = np.ones(len(x), dtype=np.float64)
     for k in range(n):
         result = result * x / (n - k)
diff --git a/testing/test_cache.py b/testing/test_cache.py
new file mode 100644
index 0000000..e69de29
diff --git a/testing/test_env.py b/testing/test_env.py
new file mode 100644
index 0000000..e69de29
diff --git a/testing/test_evaluator.py b/testing/test_evaluator.py
new file mode 100644
index 0000000..e69de29
diff --git a/testing/test_legacy.py b/testing/test_legacy.py
new file mode 100644
index 0000000..e69de29
diff --git a/testing/test_logger.py b/testing/test_logger.py
new file mode 100644
index 0000000..e69de29
diff --git a/testing/test_math.py b/testing/test_math.py
new file mode 100644
index 0000000..a1f8929
--- /dev/null
+++ b/testing/test_math.py
@@ -0,0 +1,100 @@
+import numpy as np
+import pytest
+import scgenerator.math as m
+from math import factorial
+
+
+def test__power_fact_array():
+    x = np.random.rand(5)
+    for i in range(5):
+        assert m._power_fact_array(x, i) == pytest.approx(x ** i / factorial(i))
+
+
+def test__power_fact_single():
+    pass
+
+
+def test_abs2():
+    x = np.random.rand(5)
+    assert m.abs2(5) == 25
+    assert m.abs2(2 - 2j) == 8
+    assert all(m.abs2(x) == abs(x) ** 2)
+
+
+def test_all_zeros():
+    x = np.geomspace(0.1, 1, 100)
+    y = np.sin(1 / x)
+    target = [1 / (3 * np.pi), 1 / (2 * np.pi), 1 / np.pi]
+    assert m.all_zeros(x, y) == pytest.approx(target, abs=1e-4)
+
+    x = np.array([0, 1])
+    y = np.array([-1, 1])
+    assert all(m.all_zeros(x, y) == np.array([0.5]))
+
+    x = np.array([0, 1])
+    y = np.array([1, 1])
+    assert len(m.all_zeros(x, y)) == 0
+
+
+def test_argclosest():
+    pass
+
+
+def test_build_sim_grid():
+    pass
+
+
+def test_indft():
+    pass
+
+
+def test_indft_matrix():
+    pass
+
+
+def test_jn_zeros():
+    pass
+
+
+def test_length():
+    pass
+
+
+def test_ndft():
+    pass
+
+
+def test_ndft_matrix():
+    pass
+
+
+def test_np_cache():
+    pass
+
+
+def test_power_fact():
+    pass
+
+
+def test_sigmoid():
+    pass
+
+
+def test_span():
+    pass
+
+
+def test_tspace():
+    pass
+
+
+def test_u_nm():
+    pass
+
+
+def test_update_frequency_domain():
+    pass
+
+
+def test_wspace():
+    pass
diff --git a/testing/test_operators.py b/testing/test_operators.py
new file mode 100644
index 0000000..e69de29
diff --git a/testing/test_parameter.py b/testing/test_parameter.py
new file mode 100644
index 0000000..e69de29
diff --git a/testing/test_pbar.py b/testing/test_pbar.py
new file mode 100644
index 0000000..e69de29
diff --git a/testing/test_plotting.py b/testing/test_plotting.py
new file mode 100644
index 0000000..e69de29
diff --git a/testing/test_resonance.py b/testing/test_resonance.py
index 133a193..065b541 100644
--- a/testing/test_resonance.py
+++ b/testing/test_resonance.py
@@ -1,7 +1,6 @@
 import numpy as np
 import scgenerator as sc
 import matplotlib.pyplot as plt
-from pathlib import Path
 
 
 def main():
diff --git a/testing/test_spectra.py b/testing/test_spectra.py
new file mode 100644
index 0000000..e69de29
diff --git a/testing/test_utils.py b/testing/test_utils.py
new file mode 100644
index 0000000..e69de29