Fix error in test for load_fits

This was not actually testing passing in a file name...it was passing in
an HDU.

Author: mwcraig

src/astro_image_display_api/widget_api_test.py

@@ -70,9 +70,12 @@ def test_width_height(self):
         assert self.image.image_width == width
         assert self.image.image_height == height
 
-    def test_load_fits(self, data):
+    def test_load_fits(self, data, tmp_path):
         hdu = fits.PrimaryHDU(data=data)
-        self.image.load_fits(hdu)
+        image_path = tmp_path / 'test.fits'
+        hdu.header["BUNIT"] = "adu"
+        hdu.writeto(image_path)
+        self.image.load_fits(image_path)
 
     def test_load_nddata(self, data):
         nddata = NDData(data)