diff --git a/tests/test_full.py b/tests/test_full.py
index 2ec6aba..6187fb7 100644
--- a/tests/test_full.py
+++ b/tests/test_full.py
@@ -7,6 +7,7 @@ from amodem import send
 from amodem import recv
 from amodem import common
 from amodem import sigproc
+from amodem import sampling
 
 import logging
 logging.basicConfig(level=logging.DEBUG,
@@ -18,7 +19,7 @@ class Args(object):
         self.__dict__.update(kwargs)
 
 
-def run(size, chan):
+def run(size, chan=None, df=0):
     tx_data = os.urandom(size)
     tx_audio = BytesIO()
     send.main(Args(silence_start=1, silence_stop=1,
@@ -26,7 +27,13 @@ def run(size, chan):
 
     data = tx_audio.getvalue()
     data = common.loads(data)
-    data = chan(data)
+    if chan is not None:
+        data = chan(data)
+    if df:
+        sampler = sampling.Sampler(data, sampling.Interpolator())
+        sampler.freq += df
+        data = sampler.take(len(data))
+
     data = common.dumps(data)
     rx_audio = BytesIO(data)
 
@@ -37,31 +44,37 @@ def run(size, chan):
     assert rx_data == tx_data
 
 
+def test_small():
+    run(1024, chan=lambda x: x)
+
+
+def test_frequency_error():
+    for df in [1, -1, 10, -10]:
+        run(1024, df=df*1e-6)
+
+
 def test_lowpass():
-    run(1024, lambda x: sigproc.lfilter(b=[0.9], a=[1.0, -0.1], x=x))
+    run(1024, chan=lambda x: sigproc.lfilter(b=[0.9], a=[1.0, -0.1], x=x))
 
 
 def test_highpass():
-    run(1024, lambda x: sigproc.lfilter(b=[0.9], a=[1.0, 0.1], x=x))
-
-
-def test_small():
-    run(1024, lambda x: x)
-
-
-def test_large():
-    run(54321, lambda x: x)
+    run(1024, chan=lambda x: sigproc.lfilter(b=[0.9], a=[1.0, 0.1], x=x))
 
 
 def test_attenuation():
-    run(5120, lambda x: x * 0.1)
+    run(5120, chan=lambda x: x * 0.1)
 
 
 def test_low_noise():
     r = np.random.RandomState(seed=0)
-    run(5120, lambda x: x + r.normal(size=len(x), scale=0.0001))
+    run(5120, chan=lambda x: x + r.normal(size=len(x), scale=0.0001))
 
 
 def test_medium_noise():
     r = np.random.RandomState(seed=0)
-    run(5120, lambda x: x + r.normal(size=len(x), scale=0.001))
+    run(5120, chan=lambda x: x + r.normal(size=len(x), scale=0.001))
+
+
+def test_large():
+    run(54321, chan=lambda x: x)
+