Update README to document how to work with PowerMockRunner

[sbabcoc]

The native implementation of PowerMockRunner uses a deprecated JUnit runner model that JUnit Foundation doesn't support. You need to delegate test execution to the standard BlockJUnit4ClassRunner (or subclasses thereof) to enable reporting of test lifecycle events. This is specified via the @PowerMockRunnerDelegate annotation, as shown below:

package com.nordstrom.automation.junit;

import static org.hamcrest.CoreMatchers.equalTo;
import static org.hamcrest.MatcherAssert.assertThat;
import static org.mockito.Mockito.when;
import static org.powermock.api.mockito.PowerMockito.mockStatic;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.BlockJUnit4ClassRunner;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;
import org.powermock.modules.junit4.PowerMockRunnerDelegate;

@RunWith(PowerMockRunner.class)
@PowerMockRunnerDelegate(BlockJUnit4ClassRunner.class)
@PrepareForTest(PowerMockCases.StaticClass.class)
public class PowerMockCases {

    @Test
    public void testHappyPath() {
        mockStatic(StaticClass.class);
        when(StaticClass.staticMethod()).thenReturn("mocked");
        assertThat(StaticClass.staticMethod(), equalTo("mocked"));
    }

    static class StaticClass {
        public static String staticMethod() {
            return null;
        }
    }
}