Mocking static method calls with Powermock vs. simple POJOs

pojo Configuration.java

package de.tk.mocks.staticaccess.custommock;

import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

public class Configuration {

    private SystemPropertyAccessor systemProperties;
    private Properties properties = new Properties();

    public Configuration() {
        this(new SystemPropertyAccessor());
    }

    public Configuration(SystemPropertyAccessor systemProperties) {
        this.systemProperties = systemProperties;
        try {
            InputStream configFile = getClass().getResourceAsStream(
                    "/config.properties");
            if (configFile == null)
                reportMissingConfigurationFile();
            properties.load(configFile);
        } catch (IOException e) {
            reportMissingConfigurationFile();
        }
    }

    private void reportMissingConfigurationFile() {
        throw new RuntimeException(
                "could not load properties from /config.properties");
    }

    public String getValue(String key) {
        String valueFromSystem = systemProperties.get(key);
        return valueFromSystem == null ? properties.getProperty(key)
                : valueFromSystem;
    }
}

pojo ConfigurationTest.java

package de.tk.mocks.staticaccess.custommock;

import static org.hamcrest.Matchers.equalTo;
import static org.junit.Assert.assertThat;

import org.junit.Before;
import org.junit.Test;

public class ConfigurationTest {
    private static final String KEY = "example.key";
    private Configuration config;

    @Before
    public void setUp() {
        config = new Configuration();
    }

    @Test
    public void returnsValueFromProperties() throws Exception {
        assertThat(config.getValue(KEY), equalTo("original value"));
    }

    @Test
    public void prefersSystemPropertiesOverValuesFromConfigFile()
            throws Exception {

        SystemPropertyAccessor accessorMock = new SystemPropertyAccessor() {
            @Override
            public String get(String key) {
                if (KEY.equals(key))
                    return "mocked value";
                return super.get(key);
            }
        };

        Configuration config = new Configuration(accessorMock);
        assertThat(config.getValue(KEY), equalTo("mocked value"));
    }
}

pojo SystemPropertyAccessor.java

package de.tk.mocks.staticaccess.custommock;

public class SystemPropertyAccessor {
    public String get(String key) {
        return System.getenv(key);
    }
}

pom.xml

[...]
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.11</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.hamcrest</groupId>
            <artifactId>hamcrest-all</artifactId>
            <version>1.3</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.powermock</groupId>
            <artifactId>powermock-module-junit4</artifactId>
            <version>1.5.1</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.powermock</groupId>
            <artifactId>powermock-api-mockito</artifactId>
            <version>1.5.1</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
[...]

powermock Configuration.java

package de.tk.mocks.staticaccess.powermock;

import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

public class Configuration {

    private Properties properties = new Properties();

    public Configuration() {
        try {
            InputStream configFile = getClass().getResourceAsStream(
                    "/config.properties");
            if (configFile == null)
                reportMissingConfigurationFile();
            properties.load(configFile);
        } catch (IOException e) {
            reportMissingConfigurationFile();
        }
    }

    private void reportMissingConfigurationFile() {
        throw new RuntimeException(
                "could not load properties from /config.properties");
    }

    public String getValue(String key) {
        String valueFromSystem = System.getProperty(key);
        return valueFromSystem == null ? properties.getProperty(key)
                : valueFromSystem;
    }
}

powermock ConfigurationTest.java

package de.tk.mocks.staticaccess.powermock;

import static org.hamcrest.Matchers.equalTo;
import static org.junit.Assert.assertThat;
import static org.mockito.Matchers.anyString;

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.Mockito;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;

@RunWith(PowerMockRunner.class)
@PrepareForTest({ System.class, Configuration.class })
public class ConfigurationTest {

    private static final String KEY = "example.key";
    private Configuration config;

    @Before
    public void setUp() {
        config = new Configuration();
    }

    @Test
    public void returnsValueFromProperties() throws Exception {
        assertThat(config.getValue(KEY), equalTo("original value"));
    }

    @Test
    public void prefersSystemPropertiesOverValuesFromConfigFile()
            throws Exception {

        PowerMockito.mockStatic(System.class);
        Mockito.when(System.getProperty(KEY)).thenReturn("mocked value");

        assertThat(config.getValue(KEY), equalTo("mocked value"));
    }
}