How to test methods that output/input to/from a file

[civic lark]

I currently have a shell app that takes commands and either reads from a file or writes to a path. My question is, what is the best way to write those methods to be testable? For example, here is my method that reads from a file:

  @Command(command = "load", description = "Load configuration from file")
  public void loadConfig(
      @Option(longNames = "path", shortNames = 'p', required = true) String path) {
    Path filePath = Path.of(System.getProperty("user.dir"), path);
    try {
      InputStream input = new FileInputStream(filePath.toFile());
      Table table = tableLoader.loadTableConfig(input);
      dataManager.addTable(table);
    } catch (IOException e) {
      log.error(e);
    }
  }

Here's the method that writes to a file:

  public void writeConfig(
      @Option(longNames = "path", shortNames = 'p', required = true) String path,
      @Option(longNames = "table", shortNames = 't', required = true) String tableName) {
    Path filePath = Path.of(System.getProperty("user.dir"), path);
    try {
      OutputStream input = new FileOutputStream(filePath.toFile());
      Table table = dataManager.getTable(tableName);
      tableLoader.writeTableConfig(input, table);
    } catch (IOException e) {
      log.error(e);
    }
  }

(Also, I didn't know the best way to read relative file paths from the directory the program is run in so if this is bad practice, please let me know)

[errant gorge]

Detected code, here are some useful tools:

Formatted code

@Command(command = "load", description = "Load configuration from file") public void loadConfig(@Option(longNames = "path", shortNames = 'p', required = true) String path) {
  Path filePath = Path.of(System.getProperty("user.dir"), path);
  try {
    InputStream input = new FileInputStream(filePath.toFile());
    Table table = tableLoader.loadTableConfig(input);
    dataManager.addTable(table);
  } catch (IOException e) {
    log.error(e);
  }
}

<@&1004656351647117403> please have a look, thanks.

[proud sonnet]

Split the methods...

@Command(command = "load", description = "Load configuration from file")
public void loadConfig(
    @Option(longNames = "path", shortNames = 'p', required = true)
    String path) {

    try (InputStream input = Files.newInputStream(Path.of(path))) {
        loadConfig(input);
    } catch (IOException e) {
        log.error(e);
    }
}

void loadConfig(InputStream input) throws IOException {
    Table table = tableLoader.loadTableConfig(input);
    dataManager.addTable(table);
}

Now your file-specific logic is separate and you can test them separately (though where you split and howm and whether you make the other method public/private might depend on your needs.

[errant gorge]

@civic lark

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[civic lark]

I could just test the tableLoader class instead of this class so maybe it doesn't make sense to test this class like that?