E.g. see:
https://ci.chromium.org/p/v8/builders/luci.v8.try/v8_android_arm64_n5x_rel_ng_triggered/b8924713574180831728

The testfilter was properly used and only one test was run. But the standard bot configuration uses 4 shards and 3 resulted in zero tests. This produces a failure error code that leads to a spurious purple step.