The test forum doesn't have the "unsolved/solved" labels.
You can change a thread from "unsolved" to "solved" (in forums that do use these labels) by editing the first post of the thread, clicking "Go Advanced" and then selecting "Solved" in the drop down window.
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You can change a thread from "unsolved" to "solved" (in forums that do use these labels) by editing the first post of the thread, clicking "Go Advanced" and then selecting "Solved" in the drop down window.