error_case 0.0.1

A library to define error use cases for Dart.

Error Case

Welcome to the error_case library. A library to define error cases that we can use to test our code.

Features

• Data class validation
• Empty string validation
• Minimum number validation
• Maximum number validation
• More to come in the future...

How to use

Let's start with an example of a data class.

class User implements JsonModel {

    User(this.id, this.name, this.address, this.age);

    final String id;
    final String name;
    final Map<String, String> address;
    final int age;

    factory User.fromJson(Map<String, dynamic> json) =>
        _$UserItemFromJson(json);

    @override
    Map<String, dynamic> toJson() => _$UserItemToJson(this);
}

In our data class User we have id, name, address, age properties. This will be our sample data class throughout the guide.

It is important to note that this implements JsonModel a class that contains fromJson() & toJson() functions.

In this example I am also using json_serializable to generate fromJson & toJson functions.

class InvalidUserModelErrorCase extends ObjectSingleErrorCase {

    InvalidUserModelErrorCase(): super(
        ['id', 'name', 'address.country', age], // Required properties
        minimumValue: {'age': 21},
        maximumValue: {'age': 200}
    );
}

// P.S. There's a shorter way to implement this but we need Dart 2.16

In our error case we've defined our required fields id, name, address.country, age.

What is address.country? This defines a nested lookup that validates the keys it passes through and value at the end.

If we don't include a property of the class. It will be considered optional, no validation will happened to that property.

Let's see a brief example of how we use these classes we've written.

void main() {

    final user = User( // Here's a sample User class
        'ABCD1234', // id
        'David Hamster', // name
        {'country': 'Kingdom of Nocturnia'}, // address map
        24 // age
    );

    const errorCase = InvalidUserModelErrorCase();

    errorCase.validate(user,
    _onInvalidUserModel,
    _onValidUserModel);
}

void _onInvalidUserModel(Exception ex) {
    // 'ex' can be a child of ErrorCaseException or a different Exception altogether.
}

void _onValidUserModel(User user) {
    // When there are no errors, the data that was validated will be passed on as a parameter for this function.
}

To summarize the example above.

• We have a user class with data.
• We create a const of an Error case.
• We then call .validate() and pass data, errorFunction, successFunction.

Non Returning Error Cases

These are error cases that do not expect a return value on the error and success functions.

Classes

• SingleErrorCase
• ObjectSingleErrorCase

See error_case_test.dart

Returning Error Cases

These are error cases that expect a return value on the error and success functions.

Classes

• SingleErrorReturnCase
• ObjectSingleErrorReturnCase

See error_case_return_test.dart

Good Practices

DO: Create a new error case class for a specific scenario. Just like when defining a Use Case for specific business logics.

DONT: Combine with other scenarios. This will make it difficult to locate where the error is happening when on reports.

--

DO: Declare a new instance of an error case with const for compile time benefits.

DONT: Declare a new instance of an error case without const on the UI code because it can be recreated.