add test on the sync timestamps linear option

setup.py

@@ -8,7 +8,7 @@
 
 setuptools.setup(
     name="ibl-neuropixel",
-    version="1.1.0a",
+    version="1.1.0a01",
     author="The International Brain Laboratory",
     description="Collection of tools for Neuropixel 1.0 and 2.0 probes data",
     long_description=long_description,

src/ibldsp/utils.py

@@ -26,7 +26,7 @@ def _interp_fcn(tsa, tsb, ib, linear=linear):
         ab = np.polyfit(tsa[ib >= 0], tsb[ib[ib >= 0]] - tsa[ib >= 0], 1)
         drift_ppm = ab[0] * 1e6
         if linear:
-            fcn_a2b = lambda x: x * ab[0] + ab[1]  # noqa
+            fcn_a2b = lambda x: x * (1 + ab[0]) + ab[1]  # noqa
         else:
             fcn_a2b = scipy.interpolate.interp1d(
                 tsa[ib >= 0], tsb[ib[ib >= 0]], fill_value="extrapolate"

src/tests/unit/cpu/test_ibldsp.py

@@ -18,7 +18,15 @@
 
 
 class TestSyncTimestamps(unittest.TestCase):
-    def test_timestamps_lin(self):
+
+    def test_sync_timestamps_linear(self):
+        ta = np.cumsum(np.abs(np.random.randn(100))) * 10
+        tb = ta * 1.0001 + 100
+        fcn, drif, ia, ib = utils.sync_timestamps(ta, tb, return_indices=True, linear=True)
+        np.testing.assert_almost_equal(drif, 100)
+        np.testing.assert_almost_equal(tb, fcn(ta))
+
+    def test_timestamps(self):
         np.random.seed(4132)
         n = 50
         drift = 17.14