How to use the gulp-append-prepend.appendText function in gulp-append-prepend

function testsBuild() {
    // Combine js files and append tests
    return gulp.src(getPaths().map(function(f) { return 'site/public/' + f; })) // Get rid of prepend
      .pipe(concat('tests/index.js'))
      .pipe(gap.prependFile('tests/prepend.js'))
      .pipe(gap.appendText('start();'))
      .pipe(addsrc.append(getTestPaths().map(function (f) { return 'tests/public/' + f; })))
      .pipe(concat('tests/index.js'))
      .pipe(gulp.dest('.'));
}

gulp.task('vendorDraftJsCss', function () {
  return gulp
    .src([`${draftJsDist}/Draft.css`])
    .pipe(gap.prependText('::ng-deep { '))
    .pipe(gap.prependText('/* This file is automatically generated from Draft.css upstream */'))
    .pipe(gap.prependText('/* Do not edit */'))
    .pipe(gap.appendText(' }'))
    .pipe(compileSass())
    .pipe(rename('draft-js.component.css'))
    .pipe(gulp.dest(`${src}/${lib}`));
});

const htmlInsert = stream => {
  current.config.htmlInsert.start && stream.pipe(gap.prependText(current.config.htmlInsert.start));
  current.config.htmlInsert.end && stream.pipe(gap.appendText(current.config.htmlInsert.end));
};

const buildJs = () =>
         gulp.src('dna.js')
            .pipe(replace(headerComments.js, ''))
            .pipe(header(bannerJs))
            .pipe(replace('[VERSION]', pkg.version))
            .pipe(size({ showFiles: true }))
            .pipe(gulp.dest('dist'))
            .pipe(babel(babelMinifyJs))
            .pipe(rename({ extname: '.min.js' }))
            .pipe(header(bannerJs))
            .pipe(gap.appendText('\n'))
            .pipe(size({ showFiles: true }))
            .pipe(gulp.dest('dist'));
      return mergeStream(buildCss(), buildJs());

buildDistribution: () => {
      return gulp.src('fetch-json.js')
         .pipe(replace(headerComments, ''))
         .pipe(header(bannerJs))
         .pipe(replace('[VERSION]', pkg.version))
         .pipe(size({ showFiles: true }))
         .pipe(gulp.dest('dist'))
         .pipe(babel(babelMinifyJs))
         .pipe(rename({ extname: '.min.js' }))
         .pipe(header(bannerJs))
         .pipe(gap.appendText('\n'))
         .pipe(size({ showFiles: true }))
         .pipe(size({ showFiles: true, gzip: true }))
         .pipe(gulp.dest('dist'));
      }
   };

function runSass() {
  return gulp
    .src('src/**/!(shared-styles).scss')
    .pipe(sass())
    .pipe(gap.prependText(scssFileHeader))
    .pipe(gap.appendText(scssFileFooter))
    .pipe(rename({ extname: '-css.ts' }))
    .pipe(gulp.dest('src/'));
}

buildDistribution: () => {
      return gulp.src('clabe.js')
         .pipe(replace(headerComments, ''))
         .pipe(header(bannerJs))
         .pipe(replace('[VERSION]', pkg.version))
         .pipe(size({ showFiles: true }))
         .pipe(gulp.dest('dist'))
         .pipe(babel(babelMinifyJs))
         .pipe(rename({ extname: '.min.js' }))
         .pipe(header(bannerJs))
         .pipe(gap.appendText('\n'))
         .pipe(size({ showFiles: true }))
         .pipe(size({ showFiles: true, gzip: true }))
         .pipe(gulp.dest('dist'));
      }
   };

gulp.task('js-webpack', function(){
	gulp.src('./js/*.js')
		.pipe(strip())
		.pipe(rename({
			suffix: '-webpack'
		}))
		.pipe(gap.appendText('export default Canvi;'))
		.on('error', function (err) { gutil.log(gutil.colors.red('[Error]'), err.toString()); })
		.pipe(gulp.dest('dist'));
});