Junit5 mock a static method

The short answer is no, as the Mockito team is done with their work and is waiting for the JUnit team for an extension and are discussing here a lot.

With some overhead you can: As JUnit 5 provides support for running legacy JUnit 4, and there you can use Mockito. So you can create tests in Junit4 for these cases:

A sample project for migration setup with gradle and with mvn. From there I am using PowerMock 2.0 beta with Mockito 2.

The reason why Mockito doesn't provide static methods mocking at the moment is because of the common belief that static method shouldn't need to be mocked.

However, there is an open item for Mockito here that discusses the issue.

While this doesn't answer your question, in general it tells you why you shouldn't need the feature at all or will allow you to join the conversation with your ideas.

From Mockito 3.4.0 (2020-07-10), it is possible to mock static methods out of the box even in JUnit 5, without any extension.

In the documentation, you can find an example: 48. Mocking static methods (since 3.4.0)

Important note: You need to use inline mock maker. So the dependency to use is not the core one:

        <dependency>
            <groupId>org.mockito</groupId>
            <artifactId>mockito-inline</artifactId>
            <version>3.4.6</version>
            <scope>test</scope>
        </dependency>

Example: Class under test:

package teststatics;

public class FooWithStatics {
    public static Long noParameters() {
        return System.currentTimeMillis();
    }
    public static String oneParameter(String param1) {
        return param1.toUpperCase();
    }
}

Test class:

package teststatics;

import org.junit.jupiter.api.Test;
import org.mockito.MockedStatic;

import static org.junit.jupiter.api.Assertions.*;
import static org.mockito.Mockito.*;

public class FooWithStaticsTest {

    @Test
    void testStatic() {
        // Before mock scope, usual behavior.
        assertNotEquals(0L, FooWithStatics.noParameters());
        assertNotEquals("yyy", FooWithStatics.oneParameter("xxx"));

        // Mock scope
        try (MockedStatic mocked = mockStatic(FooWithStatics.class)) {

            // Mocking
            mocked.when(FooWithStatics::noParameters).thenReturn(0L);
            mocked.when(() -> FooWithStatics.oneParameter("xxx")).thenReturn("yyy");

            // Mocked behavior
            assertEquals(0L, FooWithStatics.noParameters());
            assertEquals("yyy", FooWithStatics.oneParameter("xxx"));

            // Verifying mocks.
            mocked.verify(times(1), FooWithStatics::noParameters);
            mocked.verify(times(1), () -> FooWithStatics.oneParameter("xxx"));
        }

        // After mock scope returns to usual behavior.
        assertNotEquals(0L, FooWithStatics.noParameters());
        assertNotEquals("yyy", FooWithStatics.oneParameter("xxx"));
    }
}