Why does height 100% not work on a parent with a min-height?

Parent has height: 50vh, child has 100% height, and it's working as expected.

.parent {
    height: 50vh;
    border: 2px solid red;
}

.child {
    height: 100%;
    border: 2px solid blue;
}

<div class="parent">
    <div class="child">test</div>
</div>

Parent has min-height: 50vh, child has 100% height, and it' not working.

.parent {
    min-height: 50vh;
    border: 2px solid red;
}

.child {
    height: 100%;
    border: 2px solid blue;
}

<div class="parent">
    <div class="child">test</div>
</div>

Why?