You would want to check if there is a length of the item. The field exists, so isDefined
will always return true
<cfloop query="GetMyList1">
<tr>
<td align="center">#GetMyList1.TestName#</td>
<td align="center"><cfif len(trim(GetMyList1.TestNumber))>#GetMyList1.TestNumber#<cfelse>N/A</cfif></td>
<td align="center">#GetMyList1.Date#</td>
</tr>
</cfloop>