[FIXED] How do I test this function using mockito and junit?

Issue

I'm new to mockito and junit5. I'm trying to test the below function:

public boolean checkFunction(String element) {

        CloseableHttpClient client = HttpClients.createDefault();
        String uri = "any url im hitting";
    
        HttpPost httpPost = new HttpPost(uri);

        String json = element;

        StringEntity entity;

        try {
            entity = new StringEntity(json);
            httpPost.setEntity(entity);
            httpPost.setHeader("Accept", "application/json");
            httpPost.setHeader("Authorization", "any token");

            CloseableHttpResponse response = client.execute(httpPost);
            String responseBody = EntityUtils.toString(response.getEntity());
            client.close();

            if (responseBody.contains("any string i wanna check"))
                return true;
        } catch (Exception e) {
            return false;
        }
        return false;
    }

I tried the below code but I'm unable to get entire code coverage. Also I don't think this is the right approach.

@Test
    public void testCheckFunction() throws Exception {
        when(mockClass.checkFunction(Mockito.anyString())).thenReturn(false);
        assertEquals(false, mockclass.checkFunction("dummy"));
    }

Can anyone help me with this? Thanks!

Solution

First you have to refactor your code for better testability:

public class Checker {

    private final CloseableHttpClient client;

    public Checker(CloseableHttpClient client) {
        this.client = client;
    }

    public boolean checkFunction(String element) {

        String uri = "http://example.com";

        HttpPost httpPost = new HttpPost(uri);

        String json = element;

        StringEntity entity;

        try {
            entity = new StringEntity(json);
            httpPost.setEntity(entity);
            httpPost.setHeader("Accept", "application/json");
            httpPost.setHeader("Authorization", "any token");

            CloseableHttpResponse response = client.execute(httpPost);
            String responseBody = EntityUtils.toString(response.getEntity());
            client.close();

            if (responseBody.contains("any string i wanna check"))
                return true;
        } catch (Exception e) {
            return false;
        }
        return false;
    }
}

Note that the dependency (i.e. the thing that has to be mocked in tests) is now injected via the constructor. This way it can easily be replaced by a mock when unit testing this class:

class CheckerTest {

    private final CloseableHttpClient clientMock = Mockito.mock(CloseableHttpClient.class);

    private final Checker checker = new Checker(clientMock);

    @Test
    public void testCheckFunction() throws Exception {
        when(clientMock.execute(any(HttpPost.class))).thenThrow(new RuntimeException("Oops!"));
        assertFalse(checker.checkFunction("dummy"));
    }
}

Answered By - slauth