Remove PowerMock (#37)

pom.xml

@@ -4,7 +4,7 @@
   <parent>
     <groupId>org.jenkins-ci.plugins</groupId>
     <artifactId>plugin</artifactId>
-    <version>4.25</version>
+    <version>4.26</version>
     <relativePath />
   </parent>
 
@@ -60,11 +60,6 @@
       <artifactId>hamcrest-core</artifactId>
       <scope>test</scope>
     </dependency>
-    <dependency>
-      <groupId>org.powermock</groupId>
-      <artifactId>powermock-module-junit4</artifactId>
-      <scope>test</scope>
-    </dependency>
   </dependencies>
 
   <repositories>

src/test/java/org/jenkinsci/plugins/resourcedisposer/AsyncResourceDisposerTest.java

@@ -52,9 +52,9 @@
 import org.jvnet.hudson.test.Issue;
 import org.jvnet.hudson.test.JenkinsRule;
 import org.jvnet.hudson.test.MockAuthorizationStrategy;
-import org.powermock.reflect.Whitebox;
 
 import java.io.IOException;
+import java.lang.reflect.Field;
 import java.net.URL;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -188,7 +188,7 @@ public void showProblems() throws Exception {
         HtmlPage manage = wc.goTo("manage");
         assertThat(manage.asText(), not(containsString("There are resources Jenkins was not able to dispose automatically")));
 
-        Whitebox.setInternalState(disposer.getBacklog().iterator().next(), "registered", new Date(0)); // Make it decades old
+        setInternalState(disposer.getBacklog().iterator().next(), "registered", new Date(0)); // Make it decades old
 
         assertTrue(disposer.isActivated());
         manage = wc.goTo("manage");
@@ -367,6 +367,12 @@ public void preventLivelockWithManyStalledInstances() throws Throwable {
         assertThat(disposer.getBacklog(), iterableWithSize(MPS));
     }
 
+    private void setInternalState(Object obj, String fieldName, Object newValue) throws NoSuchFieldException, IllegalAccessException {
+        Field field = obj.getClass().getDeclaredField(fieldName);
+        field.setAccessible(true);
+        field.set(obj, newValue);
+    }
+
     private static final class OccupyingDisposable implements Disposable {
         private static final long serialVersionUID = 4648005477636912909L;