Fix CUNIT3 set to undefined value instead of empty string

megaradrp/processing/cube.py

@@ -311,7 +311,7 @@ def merge_wcs(hdr_sky, hdr_spec, out=None):
     c_cunit = 'Units of coordinate increment and value'
     hdr.set('CUNIT1', comment=c_cunit, after='CDELT1')
     hdr.set('CUNIT2', comment=c_cunit, after='CUNIT1')
-    hdr.set('CUNIT3', comment=c_cunit, after='CUNIT2')
+    hdr.set('CUNIT3', value='', comment=c_cunit, after='CUNIT2')
     hdr.set('CRPIX2', value=1, comment=c_crpix, after='CRPIX1')
     hdr.set('CRPIX3', value=1, comment=c_crpix, after='CRPIX2')
     hdr.set('CDELT3', after='CDELT2')

megaradrp/processing/tests/test_cube.py

@@ -1,8 +1,36 @@
+import math
+
 import pytest
 
-from ..cube import create_cube
+from ..cube import create_cube, merge_wcs
+
+
+def generate_wcs1():
+    import astropy.wcs
+
+    wcsl = astropy.wcs.WCS(naxis=2)
+
+    crpix = 3.0
+    crval = 5300.0
+    cdelt = 0.1
+
+    wcsl.wcs.crpix = [crpix, 0.0]
+    wcsl.wcs.crval = [crval, 0.0]
+    wcsl.wcs.cdelt = [cdelt, 1.0]
+    wcsl.wcs.ctype = ['RA---TAN', 'DEC--TAN']
+    ang = math.pi / 3.0
+    wcsl.wcs.pc = [[math.cos(ang), -math.sin(ang)], [math.sin(ang), math.cos(ang)]]
+    return wcsl
 
 
 def test_create_cube_raise():
     with pytest.raises(ValueError):
-        create_cube(None, None, 3)
+        create_cube(None, None, 3)
+
+
+def test_merge_wcs():
+    hdr1 = generate_wcs1().to_header()
+    hdr2 = generate_wcs1().to_header()
+    res = merge_wcs(hdr1, hdr2)
+    cunit3 = res['CUNIT3']
+    assert cunit3 == ''