Flutter: how to load file for testing

The current directory is always the project root in Flutter 2.0 🎉 So you can now read files with the same code on the command line and in the IDE.

https://github.com/flutter/flutter/pull/74622

Just had a go at this and it's easier than you might expect.

First, create a folder that lives in the same directory than your tests are. For example, I created a folder called test_resources.

Then, let's say we have the following JSON file for testing purposes.

test_resources/contacts.json

{
  "contacts": [
    {
      "id": 1,
      "name": "Seth Ladd"
    },
    {
      "id": 2,
      "name": "Eric Seidel"
    }
  ]
}

test/load_file_test.dart

We could use it for our test like so:

import 'dart:convert';
import 'dart:io';
import 'package:flutter_test/flutter_test.dart';

void main() {
  test('Load a file', () async {
    final file = new File('test_resources/contacts.json');
    final json = jsonDecode(await file.readAsString());
    final contacts = json['contacts'];

    final seth = contacts.first;
    expect(seth['id'], 1);
    expect(seth['name'], 'Seth Ladd');

    final eric = contacts.last;
    expect(eric['id'], 2);
    expect(eric['name'], 'Eric Seidel');
  });
}

i created an util because vscode and command line test base path is different

https://github.com/terryx/flutter-muscle/blob/master/github_provider/test/utils/test_path.dart

this is how i use it

https://github.com/terryx/flutter-muscle/blob/master/github_provider/test/services/github_test.dart#L13

---

Another way is to specify exact test path in command line

$ flutter test test

I encountered this same issue today. My tests passed in my IDE (Android Studio) but failed on CI. I found that the IDE wanted a non-relative path but flutter test wants a relative path. I think this is a bug and I'll be looking for the right place to report it. However, I found a crude work around for the meantime. Basically, I have a function which tries both ways to specify the file path..

import 'dart:convert';
import 'dart:io';

Future<Map<String, dynamic>> parseRawSample(String filePath,
    [bool relative = true]) async {
  filePath = relative ? "test_data/src/samples/raw/$filePath" : filePath;

  String jsonString;
  try {
    jsonString = await File(filePath).readAsString();
  } catch (e) {
    jsonString = await File("../" + filePath).readAsString();
  }
  return json.decode(jsonString);
}

much of that code is specific to my situation, but I think others could probably adapt this work around for their purposes.