Only specify the astropy table columns once. (#336)

src/hipscat_import/catalog/file_readers.py

@@ -306,7 +306,7 @@ def read(self, input_file, read_columns=None):
         table = Table.read(input_file, memmap=True, **self.kwargs)
         if read_columns:
             table.keep_columns(read_columns)
-        if self.column_names:
+        elif self.column_names:
             table.keep_columns(self.column_names)
         elif self.skip_column_names:
             table.remove_columns(self.skip_column_names)

tests/hipscat_import/catalog/test_file_readers.py

@@ -360,9 +360,17 @@ def test_read_fits_columns(formats_fits):
     frame = next(FitsReader(column_names=["id", "ra", "dec"]).read(formats_fits))
     assert list(frame.columns) == ["id", "ra", "dec"]
 
+    frame = next(FitsReader(column_names=["id", "ra", "dec"]).read(formats_fits, read_columns=["ra", "dec"]))
+    assert list(frame.columns) == ["ra", "dec"]
+
     frame = next(FitsReader(skip_column_names=["ra_error", "dec_error"]).read(formats_fits))
     assert list(frame.columns) == ["id", "ra", "dec", "test_id"]
 
+    frame = next(
+        FitsReader(skip_column_names=["ra_error", "dec_error"]).read(formats_fits, read_columns=["ra", "dec"])
+    )
+    assert list(frame.columns) == ["ra", "dec"]
+
 
 def test_fits_reader_provenance_info(tmp_path, basic_catalog_info):
     """Test that we get some provenance info and it is parseable into JSON."""