How to historically test conditions for their efficacy?

Neither version of TC2000 has any built in backtesting features. In StockFinder, backtesting is provided using BackScanner.

It is possible to visually backtest the technical (but not fundamental) portions of an EasyScan using TC2000 however as long as the EasyScan Conditions can be created using the Personal Criteria Formula Language. You could just use the current version of the formula as a Custom PCF % True Indicator (called a Custom Percent True Indicator in v7) and scroll back to the appropriate date to see if there was a spike using Pointer Mode (select the period key (.) on your keyboard to bring up Pointer Mode, selecting it again twice will disable Pointer Mode):

It is also possible to write Personal Criteria Formulas based on past dates (again, this is only for technicals). You may wist to review the following section of the Online Help Files:

Days Ago parameter

There are two distinct ways to use historical data with Personal Criteria Formulas.

Any criteria can be used to scan X number of days back by adding '.XX' where XX is equal to the number of market days past to calculate for. An example of this is (AVGC21.21), which is a 21 day moving average 21 of close, 21 days ago. This use of historical data always refers to the market day XX number of days ago (in this case, 21). If you wish to use a specific date’s data, use the option detailed below.

The other method of using historical data is by specifying a precise date in history to use. For example, (AVGC21.'11/13/08') will provide a 21 day moving average of close for November 13, 2008 (the period should be used in cases where the first method requires a period and not used when the first method does not use a period). Always confirm that the date you wish to use using this parameter was a market day.