How to test write to file in Java?

Question

I\'m beginner, and keep yourself in hands. I have some easy program, and I need do junit test for write method. I have some collection in input. How I can do this? This my

Answer 1

You probably don't need mocks at all. Try using StringWriter in your tests.

// write to file
public void write(String fileName, List figuresList) {
  try {
    Writer out = new FileWriter(new File(fileName).getAbsoluteFile());
    write(out, figuresList);
  } catch (IOException e) {
    System.out.println("Cannot write to file!");
  }
}

@VisibleForTesting void write(Writer writer, List figuresList) {
  PrintWriter out = new PrintWriter(writer);
  try {
    for (int i = 0; i < figuresList.size(); i++) {
      out.println(figuresList.get(i).toString());
    }
  } finally {
    out.close();
  }
}

@Test public void testWrite() {
  List list = Lists.newArrayList();
  list.add(...); // A
  list.add(...); // B
  list.add(...); // C
  StringWriter stringWriter = new StringWriter();
  write(stringWriter, list);
  assertEquals("A.\nB.\nC.\n", stringWriter.toString()); 
}