how to refactor a code with using constructor dependency injection when methods include dependency in dependency method?

Question

i want to refactor a code with using constructor dependency injection to used in unit tests

i not very sure i understand how to refactor code

for example

public class class1{

public int firstMethod()
{
   ...
   ...
   ...
 return secondMethod();
}

public int secondMethod()
{
 ...
   ...
   ...
 return thirdMethod();
}

public int thirdMethod()
{
...
   ...
   ...
 return fourthMethod();
}

public int fourthMethod()
{
int a;
...
   ...
   ...
return a;
}

if i want to refactor a code that have all this dependeinces(one include one) with constructor dependency injection for unit tests all the 4 methods

i think to do a interface for every method(4 interfaces)

and implements first interface with a constructor that get a impelements class of interface 2

is this a good Idea or i should make something else

thanks.