@fishscience you can ptovide the trigger condition as follows, please replace Columnnamehere with the name of your lookup column. Please note that this should be internal name of the column.
To get internal name of column go to your list/library settings, click on column and then see the browser URL and you will find column name after Field=, e.g. if it is Field=Title, then internal name of column is Title.
@equals(triggerBody()?['ColumnNameHere']?['Value'], 'test')
In addition to this i would suggest to use When item or file is modified trigger, configure trigger condition, then add Get Changes for an item or file action, configure it as shown in below screenshot. Then add condition action to check if lookup column column value has changed, so you can select Has Column Changed: <lookup column name> in condition in left side of condition and select true from dynamic content -> expression on right side of condition, please take a look at screenshot below. Please note to use this approach you need to enable versioning on your library.
