add tests

specreduce/tests/test_background.py

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+import numpy as np
+
+import astropy.units as u
+from astropy.nddata import CCDData
+
+from specreduce.background import Background
+from specreduce.tracing import FlatTrace
+
+
+# Test image is comprised of 30 rows with 10 columns each. Row content
+# is row index itself. This makes it easy to predict what should be the
+# value extracted from a region centered at any arbitrary Y position.
+image = np.ones(shape=(30, 10))
+for j in range(image.shape[0]):
+    image[j, ::] *= j
+image = CCDData(image, unit=u.Jy)
+
+
+def test_background():
+    #
+    # Try combinations of extraction center, and even/odd
+    # extraction aperture sizes.
+    #
+    trace_pos = 15.0
+    trace = FlatTrace(image, trace_pos)
+    bkg_sep = 5
+    bkg_width = 2
+    # all the following should be equivalent:
+    bg1 = Background(image, [trace-bkg_sep, trace+bkg_sep], width=bkg_width)
+    bg2 = Background.two_sided(image, trace, bkg_sep, width=bkg_width)
+    bg3 = Background.two_sided(image, trace_pos, bkg_sep, width=bkg_width)
+    assert np.allclose(bg1.bkg_array, bg2.bkg_array)
+    assert np.allclose(bg1.bkg_array, bg3.bkg_array)
+
+    # test that creating a one_sided background works
+    Background.one_sided(image, trace, bkg_sep, width=bkg_width)
+
+    # test that image subtraction works
+    sub1 = image - bg1
+    sub2 = bg1.sub_image(image)
+    sub3 = bg1.sub_image()
+    assert np.allclose(sub1, sub2)
+    assert np.allclose(sub1, sub3)