A test tells me it works. A volume test tells me how far it can go.

The first question

I checked whether the application opened, calculated, saved, and returned the expected result. That proved the application worked for the data I had in front of me. It did not tell me what would happen after months or years of use.

The second question

I started with a few records and increased the volume gradually. With a few thousand records, the application worked well. With a few hundred thousand, it slowed down. Around one million, it stopped responding.

Why the difference matters

A functional test checks the result for one case. A volume test shows the curve: how time, memory, and stability change as data or repetitions grow. The limit was much closer than I had hoped, but I found it at home before delivery instead of leaving the client to discover it later.

What remained

I kept the same question through Access, SQL Server, ASP, C#, SharePoint, cloud services, and AI-assisted work. The technology changed. The questions about volume, width, waiting time, repetition, and verified output remained.

A test tells me that the application works. A volume test tells me how far it can go.