Normally Test Effort is 40 of the total Actual Development effort.

For Example:

Estimated Total no of Development efforts (Man Days) - 200

Estimated test efforts as per the industry standard which is taken as 40 of
total dev efforts ( Man Days) - 80

There are different kind of approach to estimate the cost

* Percentage-of-Development Approach

* Implicit Risk Context Approach

* Metrics-Based Approach

* Test Work Breakdown Approach

* Iterative Approach

I'm not sure I fully understand the question but I will take a stab at this:

In our group the testing effort is generally considered to be 30 percent of the total development effort in terms of resources when all of the deliverables are properly and thoroughly provided to the test team. These deliverables include requirements and specifications.

"Requirements" refers to the business requirements of the program
"Specifications" refers to the technical specifications of the program

In our group it is a bonus if we receive usecases. Typically this isn't necessary when a complete and thorough listing of requirements have been provided.

1. If the client only has the high level requirements then it depends on how "high" the requirements truly are. If the requirements are so high that all of the necessary test cases can not be reasonably produced with the information given then extra effort will be needed to query for more complete requirements. If testers must ask specific questions because details are not fully explained in the requirements this will necessarily incur an increase in test time and resources.

Likewise the test team has not been given technical specifications for the program. This will incur even more test time and resources when questions are raised such as "What is the maximum number of characters users can enter in this text box?" or "Are users required to enter a phone number in any particular format?"

In scenario 1 the testing effort estimation is much greater than 30 percent and its specific value depends on information that has not been divulged.

2. If the client only has a prototype the test team will make it clear that it can not verify whether the program meets company business needs because there are no requirements. Without requirements the test team can only ensure that the program is stable and user-friendly. The test team may push back and let project manager/marketing/engineering know that it does not recommend an appreciable amount of test effort be applied to the project until requirements are provided. If the test team is compelled to devote a full test run on the project then it must be made clear that test will not endorse (sign off) on the project and will have to test the program again when the requirements are furnished to the test team. This being the case significantly more test time and resources will need to be applied to the project.

As we saw earlier even more test time and effort will be needed when questions arise due to the lack of technical specifications.

In scenario 2 the testing effort estimation is much greater than 30 percent and its specific value depends on information that has not been divulged.

3. If the client furnishes usecases and if the usecases were based on business requirements then test will need to verify whether all of the requirements were covered in the usecases. If not then more test time and effort will be needed to ask the appropriate questions to fill the gap of missing requirements. If the usecases cover all the requirements and if we can get project manager/marketing/engineering to confirm and sign off on this then test can begin authoring test cases based on the use cases.

Yet as we saw earlier more test time and effort will be needed when questions arise due to the lack of technical specifications.

In scenario 3 the testing effort estimation is greater than 30 percent but less than scenarios 1 and 2. Still its specific value depends on information that has not been divulged.

4. If the client provides the requirements and usecases then we are still missing the technical specifications. Yet this scenario gets us closest to the test team's resources being 30 percent of total development cost. Nevertheless it is still over 30 percent.