Kotlin 的“as”转换运算符如何影响分支覆盖率？

Question

How can I achieve branch coverage for an expression in which the "as" casting has been used, in this code for the expression errorCode = result.data as Int

Answer 1

This bug fix in the Jacoco (version0.8.8 Changelog ) coverage tool offers an explanation:

Branch added by the Kotlin compiler version 1.6.0 and above for "unsafe" cast operator is filtered out during generation of report (GitHub 1266 )

Thus, the Kotlin compiler may generate a hidden branch for the cast (checking whether the cast is possible at all) which then surfaces in the coverage tool used.

From a functional perspective, you may want to add a test case that covers the situation that result.data doesn't contain an int. That would probably lead to full coverage of the cast statement as well.

Though I am not a Kotlin developer, the unsafe cast raises the following questions:

1. The null != errorCode check suggests that errorCode is of type Int? and not of type Int which can never be null.
2. This also suggests the type cast can be safe, via result.data as? Int result.data as? Int , where the as? operator returns null on failure.
3. Interestingly the coverage of your null != errorCode if-condition suggests that both the true and false branch are covered. I doubt this is the case. Instead, the compiler may have concluded that the condition can never be false (since errorCode has the non nullable type Int ), and therefore optimized the else branch away.

In other words, switching to Int? and as? will likely move the reported uncovered branch to your null != errorCode if-condition, where it makes more sense.