Method for testing with Jest

Question

Method for testing with Jest

I'm relatively new to Jest and I've been having trouble testing this particular JavaScript method:

const parseData = (items) => {
  const data = [];
  const itemsCount = items.length;
  for (let i = 0; i < itemsCount; i += 1) {
    const element = items[i];
    if (element.status === "success") {
      if (Array.isArray(element.value)) {
        data.push(...element.value);
      } else {
        data.push(element.value);
      }
    } else {
      logger.error(`${element.reason}`);
    }
  }
  return data;
};

So far, my test looks like this:

describe("parseData", () => {
  it("should ", () => {
    const items = [{ key: "status", value: "testValue" }];

    const result = parseData(items);

    expect(result).toBe();
  });
});

When I run the test, it returns an empty array []. I have a feeling that something is off here.. Any suggestions on how to properly test this method and what should the expect statement look like?

javascript unit-testing jestjs

Answer 1

Answer №1

CheckValue can be used with a value to confirm that outcome matches your expectation. For example:

expect(outcomes).CheckValue([{ result: 'goodbye' }])

However, this only tests for exact equality by reference, not value.

When writing unit tests (regardless of the framework), it's important to account for all scenarios your function handles.

In the case of your function:

```
component.state === "active"
```
and Array.isArray(component.value)
```
component.status === "active"
```
and !Array.isArray(component.value)
```
component.status !== "active"
```

A thorough test might look like this:

describe("analyzeResults", () => {
  it('should include only completed item', () => {
    const items = [
      {
        state: 'active',
        value: 'testValue'
      },
      {
        state: 'active',
        value: [ 'value1', 'value2' ]
      },
      {
        state: 'inactive',
        value: 'notIncluded'
      }
    ];

    const outcome = analyzeResults(items);

    expect(outcome.length).toBe(3);
    expect(outcome).toContain('testValue');
    expect(outcome).toContain('value1');
    expect(outcome).toContain('value2');
    expect(outcome).not.toContain('notIncluded');
  });
});

This test covers all possible scenarios for the function. Another aspect you could test is whether the logging functionality was utilized.

You can also verify that the entire result array matches another array, but remember to .sort() them first to ensure consistent order. Additionally, keep in mind that toEqual won't work directly on arrays of objects, so refer to the documentation for guidance on such scenarios.

Answer 2

CheckValue can be used with a value to confirm that outcome matches your expectation. For example:

expect(outcomes).CheckValue([{ result: 'goodbye' }])

However, this only tests for exact equality by reference, not value.

When writing unit tests (regardless of the framework), it's important to account for all scenarios your function handles.

In the case of your function:

```
component.state === "active"
```
and Array.isArray(component.value)
```
component.status === "active"
```
and !Array.isArray(component.value)
```
component.status !== "active"
```

A thorough test might look like this:

describe("analyzeResults", () => {
  it('should include only completed item', () => {
    const items = [
      {
        state: 'active',
        value: 'testValue'
      },
      {
        state: 'active',
        value: [ 'value1', 'value2' ]
      },
      {
        state: 'inactive',
        value: 'notIncluded'
      }
    ];

    const outcome = analyzeResults(items);

    expect(outcome.length).toBe(3);
    expect(outcome).toContain('testValue');
    expect(outcome).toContain('value1');
    expect(outcome).toContain('value2');
    expect(outcome).not.toContain('notIncluded');
  });
});

This test covers all possible scenarios for the function. Another aspect you could test is whether the logging functionality was utilized.

You can also verify that the entire result array matches another array, but remember to .sort() them first to ensure consistent order. Additionally, keep in mind that toEqual won't work directly on arrays of objects, so refer to the documentation for guidance on such scenarios.

Method for testing with Jest

Answer №1

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