How to throw UnsupportedEncodingException in JUnit Test?

Question

I have the following implementation as follows:

public String encodeString(String testString) {

    try {
        return URLEncoder.encode(testString, "UTF-8");
    } catch (UnsupportedEncodingException e) {         <= I want to test this exception but was not successful
        log.error(ex.getMessage());
    }

    return "";
}

I have tried to write junit test for the implementation, the test did not fail but was not able to throw the exception as intended.

@Test
public void testEncodeString_Exception() throws UnsupportedEncodingException {
    // Setup
    final String testString= "U+FFFD";

    PowerMockito.mockStatic(URLEncoder.class);
    PowerMockito.when(URLEncoder.encode(testString, "UTF-8")).thenThrow(UnsupportedEncodingException.class);

    // Run the test
    final String result = classInstance.encodeString(testString);

    // Verify the results
}

I would greatly appreciate any form of help or sharing of knowledge if you have encountered the following issue previously. Thank you!

Answer 1

You should use the @PrepareForTest({URLEncoder.class}) annotation on the class level to tell PowerMockito that we need to manipulate byte codes of the URLEncoder class.

If you don't do that, there is no way PowerMockito is able to mock a static method.