elm-optimize-level-2/test/helpers/transformCode.ts

import ts from 'typescript';

export function transformCode(
  initialCode: string,
  expectedCode: string,
  transformer: ts.TransformerFactory<ts.SourceFile>
): {
  actual: string;
  expected: string;
} {
  const source = ts.createSourceFile(
    'elm.js',
    initialCode,
    ts.ScriptTarget.ES2018
  );

  const printer = ts.createPrinter();

  const [output] = ts.transform(source, [transformer]).transformed;

  const expectedOutput = printer.printFile(
    ts.createSourceFile('elm.js', expectedCode, ts.ScriptTarget.ES2018)
  );

  const printedOutput = printer.printFile(output);

  return {
    actual: printedOutput,
    expected: expectedOutput,
  };
}