addPartialTextStream(func) {
    const ContentType = shaka.util.ManifestParserUtils.ContentType;

    const stream = new shaka.test.ManifestGenerator.Stream(
        this, /* isPartial= */ true, null, ContentType.TEXT);
    if (func) {
      func(stream);
    }

    const streamObj = /** @type {shaka.extern.Stream} */ (
      jasmine.objectContaining(stream.build_()));
    this.textStreams.push(streamObj);
  }
Adds a "partial" stream which, when used with jasmine, will only compare
the properties that were explicitly given to it.  All other properties will
be ignored.

@param {function(!shaka.test.ManifestGenerator.Stream)} func