title: Bazel error: "No test targets were found, yet testing was requested"
body: <p>I have a small assignment where I used TensorFlow to create music:</p>
  
  <p><a href="https://github.com/tensorflow/magenta" rel="nofollow noreferrer">https://github.com/tensorflow/magenta</a></p>
  
  <p>When I run the code <code>--- bazel test //magenta:all</code>
  I get the following error:</p>
  
  <pre>
  WARNING: /home/admin/.cache/bazel/_bazel_admin/fb30f33370a5b97d4f9b1dde06f8f344/external/protobuf/protobuf.bzl:90:19: Variables HOST_CFG and DATA_CFG are deprecated in favor of strings "host" and "data" correspondingly.
  WARNING: /home/admin/.cache/bazel/_bazel_admin/fb30f33370a5b97d4f9b1dde06f8f344/external/protobuf/protobuf.bzl:96:28: Variables HOST_CFG and DATA_CFG are deprecated in favor of strings "host" and "data" correspondingly.
  INFO: Found 2 targets and 0 test targets...
  INFO: Elapsed time: 4.977s, Critical Path: 0.66s
  ERROR: No test targets were found, yet testing was requested.</pre>