diff --git a/pytest/test_fd.py b/pytest/test_fd.py
new file mode 100644
index 0000000..7cbc52d
--- /dev/null
+++ b/pytest/test_fd.py
@@ -0,0 +1,64 @@
+import pytest
+import numpy as np
+from GENetLib.fd import fd
+from GENetLib.create_basis import create_bspline_basis
+
+# Test fd function with default coefficients
+def test_fd_default_coef():
+    basisobj = create_bspline_basis(rangeval=[0, 1], nbasis=4, norder=4)
+    fdobj = fd(basisobj=basisobj)
+    assert 'coefs' in fdobj
+    assert fdobj['coefs'].shape == (4,)
+
+# Test fd function with custom coefficients
+def test_fd_custom_coef():
+    basisobj = create_bspline_basis(rangeval=[0, 1], nbasis=4, norder=4)
+    coef = np.random.rand(4)
+    fdobj = fd(coef=coef, basisobj=basisobj)
+    assert 'coefs' in fdobj
+    assert np.all(fdobj['coefs'] == coef)
+
+# Test fd function with multidimensional coefficients
+def test_fd_multidim_coef():
+    basisobj = create_bspline_basis(rangeval=[0, 1], nbasis=4, norder=4)
+    coef = np.random.rand(4, 2)
+    fdobj = fd(coef=coef, basisobj=basisobj)
+    assert 'coefs' in fdobj
+    assert fdobj['coefs'].shape == (4, 2)
+
+# Test fd function with invalid coefficient type
+def test_fd_invalid_coef_type():
+    basisobj = create_bspline_basis(rangeval=[0, 1], nbasis=4, norder=4)
+    coef = "not a number"
+    with pytest.raises(ValueError):
+        fd(coef=coef, basisobj=basisobj)
+
+# Test fd function with invalid coefficient dimension
+def test_fd_invalid_coef_dim():
+    basisobj = create_bspline_basis(rangeval=[0, 1], nbasis=4, norder=4)
+    coef = np.random.rand(4, 2, 2)
+    with pytest.raises(ValueError):
+        fd(coef=coef, basisobj=basisobj)
+
+# Test fd function with custom fdnames
+def test_fd_custom_fdnames():
+    basisobj = create_bspline_basis(rangeval=[0, 1], nbasis=4, norder=4)
+    coef = np.random.rand(4)
+    fdnames = {"args": ["time"], "reps": ["rep1"], "funs": ["value"]}
+    fdobj = fd(coef=coef, basisobj=basisobj, fdnames=fdnames)
+    assert 'fdnames' in fdobj
+    assert fdobj['fdnames'] == fdnames
+
+# Test fd function without basis object
+def test_fd_without_basisobj():
+    coef = np.random.rand(4)
+    fdobj = fd(coef=coef)
+    assert 'coefs' in fdobj
+    assert fdobj['coefs'].shape == (4,)
+
+# Test fd function with invalid basis object
+def test_fd_invalid_basisobj():
+    coef = np.random.rand(4)
+    basisobj = "not a basis object"
+    with pytest.raises(ValueError):
+        fd(coef=coef, basisobj=basisobj)