How often do Libraries change? Do Libraries need regression testing as much as programs do?

Question

I read it in a research paper published on IEEE which said that libraries dont change often and hence dont need much of regression testing. I wanted someone to verify the statement. Also, it said that Randoop was earlier developed and evaluated on libraries. Can someone verify that?

Answer 1

[The paper] said that Randoop was earlier developed and evaluated on libraries.

This is largely true not just of Randoop, but of other test generation tools such as ARTOO, Check 'n' Crash, EvoSuite, GRT, QuickCheck, etc.

The paper is "Scaling up automated test generation: Automatically generating maintainable regression unit tests for programs" (ASE 2011). Its problem statement is that test generation tools have often been applied to libraries, which are easier to handle than programs. Its contribution is showing how to extend a test generation tool (Randoop) to programs.

An example of an earlier paper that applied Randoop to libraries is "Feedback-directed random test generation" (ICSE 2007). It reports finding dozens of important, previously-unknown errors.

I read it in a research paper published on IEEE which said that libraries dont change often and hence dont need much of regression testing.

The paper does not say libraries "don't need much regression testing". It actually says, "A library is less likely to be in need of a regression test suite. Libraries rarely change, and a library is likely to already have some tests." The main point is that the Randoop tool generates tests, and such a tool is more needed for components that don't have tests. As a general rule, libraries usually already have a human-written test suite. The library is also exercised by every program that uses it. By contrast, many programs exist that don't have a test suite, or whose test suite omits large parts of the program's behavior. Test generation is more needed for such components.

This is point #5 near the end of a list of 6 reasons to motivate extending Randoop to programs. The comment makes sense in that context but not when taken out of context or misquoted. The list starts with,

Randoop was originally targeted toward detecting existing bugs in data structure libraries libraries such as the JDK's java.util. Instead, we want to extend Randoop to generate maintainable regression tests for complex industrial software systems.

Data structure libraries tend to be easier for tools to handle in several ways. ...

Returning to one of your questions, every software component -- whether a program or a library -- needs a regression test suite to be run when it changes. Running the tests gives you confidence that your changes have not broken its functionality. If you never change a component, then you don't need a regression test suite for it.

Some libraries never change (because of policy, or because there is no need to change them), and others are being constantly updated.