diff --git a/tests/data/coordinates.csv b/tests/data/coordinates.csv
new file mode 100644
index 0000000..46a113b
--- /dev/null
+++ b/tests/data/coordinates.csv
@@ -0,0 +1,107 @@
+,East,North
+0,1324671.2,6187244.9
+1,1324671.8,6187239.9
+2,1324672.7,6187235.0
+3,1324673.5,6187230.1
+4,1324675.1,6187225.4
+5,1324677.4,6187220.9
+6,1324679.2,6187216.3
+7,1324681.5,6187211.8
+8,1324683.9,6187207.4
+9,1324686.5,6187203.2
+10,1324689.0,6187198.9
+11,1324692.3,6187195.1
+12,1324695.6,6187191.5
+13,1324698.1,6187187.1
+14,1324701.9,6187184.1
+15,1324704.2,6187179.6
+16,1324707.7,6187176.0
+17,1324710.2,6187171.7
+18,1324712.8,6187167.4
+19,1324715.1,6187163.0
+20,1324718.3,6187159.2
+21,1324721.3,6187155.3
+22,1324725.0,6187151.9
+23,1324728.0,6187147.9
+24,1324732.0,6187145.0
+25,1324736.5,6187142.8
+26,1324741.0,6187140.7
+27,1324745.9,6187140.1
+28,1324750.6,6187138.6
+29,1324755.2,6187136.8
+30,1324760.1,6187136.4
+31,1324765.1,6187136.1
+32,1324770.1,6187135.9
+33,1324774.8,6187134.2
+34,1324779.8,6187133.7
+35,1324784.8,6187133.5
+36,1324789.8,6187133.3
+37,1324794.5,6187132.1
+38,1324799.3,6187131.1
+39,1324804.0,6187129.8
+40,1324808.0,6187126.7
+41,1324811.7,6187123.3
+42,1324815.2,6187119.8
+43,1324819.1,6187116.6
+44,1324822.3,6187112.9
+45,1324825.5,6187109.0
+46,1324828.6,6187105.1
+47,1324832.3,6187101.8
+48,1324836.6,6187099.3
+49,1324840.3,6187095.9
+50,1324843.9,6187092.4
+51,1324847.2,6187088.7
+52,1324851.6,6187086.5
+53,1324856.3,6187084.6
+54,1324860.1,6187081.4
+55,1324864.8,6187079.7
+56,1324868.9,6187076.9
+57,1324872.9,6187073.9
+58,1324876.6,6187070.4
+59,1324880.4,6187067.3
+60,1324884.3,6187064.1
+61,1324887.6,6187060.4
+62,1324891.1,6187056.8
+63,1324894.8,6187053.5
+64,1324898.1,6187049.8
+65,1324901.7,6187046.3
+66,1324905.5,6187043.1
+67,1324909.3,6187039.9
+68,1324913.0,6187036.4
+69,1324916.4,6187032.8
+70,1324919.6,6187029.0
+71,1324923.3,6187025.6
+72,1324926.3,6187021.6
+73,1324929.4,6187017.7
+74,1324933.0,6187014.2
+75,1324936.6,6187010.8
+76,1324939.8,6187007.0
+77,1324942.7,6187002.9
+78,1324945.9,6186999.1
+79,1324948.4,6186994.8
+80,1324951.9,6186991.2
+81,1324954.9,6186987.2
+82,1324957.4,6186982.8
+83,1324960.4,6186978.9
+84,1324962.7,6186974.4
+85,1324965.8,6186970.5
+86,1324968.2,6186966.1
+87,1324971.1,6186962.0
+88,1324973.7,6186957.8
+89,1324976.4,6186953.6
+90,1324978.8,6186949.2
+91,1324981.8,6186945.2
+92,1324984.3,6186940.9
+93,1324987.0,6186936.8
+94,1324989.3,6186932.3
+95,1324992.1,6186928.1
+96,1324994.2,6186923.6
+97,1324996.7,6186919.3
+98,1324998.5,6186914.8
+99,1325001.4,6186910.7
+100,1325003.7,6186906.2
+101,1325006.8,6186902.3
+102,1325009.9,6186898.4
+103,1325012.9,6186894.4
+104,1325015.3,6186890.0
+105,1325018.9,6186886.5
diff --git a/tests/test_path_functionality.py b/tests/test_path_functionality.py
new file mode 100644
index 0000000..b9ac943
--- /dev/null
+++ b/tests/test_path_functionality.py
@@ -0,0 +1,47 @@
+import pathlib
+
+import numpy as np
+import pytest
+
+from pg_rad.dataloader import load_data
+from pg_rad.path import Path, path_from_RT90
+
+@pytest.fixture
+def test_df():
+    csv_path = pathlib.Path(__file__).parent / "data/coordinates.csv"
+    return load_data(csv_path)
+
+def test_piecewise_regression(test_df):
+    """_Verify whether the intermediate points deviate less than 0.1 SD._"""
+        
+    p_full = path_from_RT90(
+        test_df,
+        east_col="East",
+        north_col="North",
+        simplify_path=False
+    )
+ 
+    p_simpl = path_from_RT90(
+        test_df,
+        east_col="East",
+        north_col="North",
+        simplify_path=True
+    )
+
+    x_f = np.array(p_full.x_list)
+    y_f = np.array(p_full.y_list)
+
+    x_s = np.array(p_simpl.x_list)
+    y_s = np.array(p_simpl.y_list)
+
+    sd = np.std(y_f)
+
+    for xb, yb in zip(x_s[1:-1], y_s[1:-1]):
+        # find nearest original x index
+        idx = np.argmin(np.abs(x_f - xb))
+        deviation = abs(yb - y_f[idx])
+
+        assert deviation < 0.1 * sd, (
+            f"Breakpoint deviation too large: {deviation:.4f} "
+            f"(threshold {0.1 * sd:.4f}) at x={xb:.2f}"
+            )
\ No newline at end of file