Mocha Test Data Loader is a helper function to generate test cases providing different data sets to the generic testing function.
yarn add --dev @zaufi/mocha-test-data-loader
or
npm install --save-dev @zaufi/mocha-test-data-loader
Imagine you are testing the transformInput
function which gets some input and produce an output.
The simplest test plan is to feed it with various data and check the output against expected
values. Everything is fine when the input data is trivial... you can just copy-n-pasted the testing
expressions expect(transformInput('blah')).to.be.blah(...)
. But even this simplest way is getting
boring very soon if you have some non-trivial data...
The idea is to put input data into an array of literal objects and generate test cases using a user provided function. Sometimes input data could be quite complex objects. This makes tests written in this way consists of too many lines of object properties. There is a way to move this data to separate files and make the tests array much shorter.
The module exports the only function makeTestCase(collection, userTestFn)
.
Every item of the given collection must have the name
property with a short description
of the test case. The other keys properties are optional, however:
- properties which names end with
_file
will be used to load JSON data from and merge it with the object instance get passed to the user provided function. It's quite possible to have multiple properties referencing different files -- all loaded data is going to be merged into a single object and later passed to the user-provided function; - properties which names end with
_from
will be used to load JSON data from<directory-of-the-test-file>/data/<name-of-the-test-file>.d/<value>.json
, where thevalue
placeholder is a string value of the property. It is also possible to have multiple keys. All of them are going to be loaded in order of declaration, so in case of property names clash the latest value will win.
Example:
describe('demo test cases', () =>
{
const tests = [
{
// The simplest one: all data specified right here
name: 'case one'
, input: 'this is just an ordinal string'
, expected: 'this is the expected result (also string)'
}
, {
// Explicit file: data get loaded from the `test_data_file`
name: 'case two'
, test_data_file: path.join(__dir, 'case-two.json')
}
, {
// Indirect: data get loaded from `{__dirname}/data/this_test.js.d/case-three.json`
name: 'case three'
, test_data_from: 'case-three'
}
, {
// Note, the test case name also could be a part of the data file, so
// the only property you need is to specify what the file to load data from.
test_data_from: 'case-four'
}
];
makeTestCase(tests, data =>
{
// Just make sure the current literal object has all expected properties
expect(data).to.contain.all.keys(['name', 'input', 'expected']);
// Do some trivial (or not) check
expect(transformInput(data.input)).to.be.equal(data.expected);
});
}
The JSON files mentioned in example supposed to have properties input
and expected
.
Also, as noticed in the very last test case, case-four.json
should have the name
property.