[Issue 16379] New: merging coverage sometimes overwrites existing results

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=16379

          Issue ID: 16379
           Summary: merging coverage sometimes overwrites existing results
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: druntime
          Assignee: nobody at puremagic.com
          Reporter: code at dawg.eu

https://github.com/dlang/phobos/pull/4719#issuecomment-239184919

Running phobos unittests with coverage for std.json multiple times correctly
merges the results.
generated/linux/debug/64/unittest/test_runner std.json

Running std.stdio (and only that module) overwrites the std-json.lst file
before rereading this.
generated/linux/debug/64/unittest/test_runner std.stdio

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