junit4 - How to write test case for the given code using powermockito -

i want know if have code -

public class {     static string b = "hello";  public static string a() {     string b = b();     string d = d(b);     string e = e(d, b);     return e; }  public static string b() {     return b; }  public static void c(string c) {     b = c; }  public static string d(string d) {     return d; }  public static string e(string e1, string e2) {      return e1 + e2; } } 

than how write test cases using power mockito since methods static , method void too.

the first thing got need write test case method since using other methods others cover in it. can me , tell me how can test .