Unit Test for a Static class with static dictionary in C#

I am new to C# UT.

I have static class (requirement are strict).

public static class MyClass
{
public static readonly Dictionary<int, int> MyDictionary;

static MyClass()
{
MyDictionary = new Dictionary<int, int>();
}

public static void init(string filePath)  // external file path which  has key value pair
{
// Fill the dictionary
}

public static int GetValue(int key)
{
int value = -1;
//some conditional logic and then
return MyDictionary.TryGetValue(key, value);
}
}

How to do the unit test for this class and dictionary.