Add unit tests for sdr.downsample()

tests/dsp/test_downsample.py

@@ -0,0 +1,27 @@
+import numpy as np
+import pytest
+
+import sdr
+
+
+def test_exceptions():
+    x = np.random.randn(40)
+
+    with pytest.raises(TypeError):
+        # Rate must be an integer
+        sdr.downsample(x, 4.0)
+    with pytest.raises(ValueError):
+        # Rate must be positive
+        sdr.downsample(x, 0)
+
+
+def test_1():
+    """
+    Matlab:
+        >> x = 0:39;
+        >> downsample(x, 4)'
+    """
+    x = np.arange(40)
+    y = sdr.downsample(x, 4)
+    y_truth = np.array([0, 4, 8, 12, 16, 20, 24, 28, 32, 36])
+    assert np.array_equal(y, y_truth)