add support for fits: write test FITS file in setUp

tests/test_fits.py

@@ -12,6 +12,7 @@ Modified-History:
 import os
 import unittest
 
+import numpy as np
 from csst_common import fits
 
 test_fits_file = os.path.join(
@@ -22,6 +23,15 @@ test_fits_file = os.path.join(
 
 class TestFitsHeaderOps(unittest.TestCase):
 
+    def setUp(self):
+        hl = fits.HDUList(
+            [
+                fits.PrimaryHDU(),
+                fits.ImageHDU(data=np.random.randn(5, 5)),
+            ]
+        )
+        hl.writeto(test_fits_file)
+
     def test_fits_open(self):
         hl = fits.open(test_fits_file)
         self.assertIsInstance(hl, fits.HDUList)