Mock System Environment Variable In C#

Question

I want to unit test the function which creates/Updates system environment variables. So how do i test the above functions using Nunit in C#?

Answer 1

Wrap the real calls that create/update the environment variables in class that can be dependency injected into your code. The two calls you need are:

string value = Environment.GetEnvironmentVariable("variableName")

Environment.SetEnvironmentVariable("variableName", "value");

This latter always takes a string as the value.

Then the wrapper class will look something like this:

class MyEnvironment
{
    public string GetVariable(string variableName)
    {
        return Environment.GetEnvironmentVariable(variableName);
    }

    public void SetVariable(string variableName, string value)
    {
        Environment.SetEnvironmentVariable(variableName, value);
    }
}

Then in your test suite inject the mock class that simulates the creation/updating. This will test the logic of your code.

The mocked class will look something like this:

class MockEnvironment
{
    private Dictionary<string, string> _mockEnvironment;

    public string GetVariable(string variableName)
    {
        return _mockEnvironment[variableName];
    }

    public void SetVariable(string variableName, string value)
    {
        // Check for entry not existing and add to dictionary
        _mockEnviroment[variableName] = value;
    }
}

You need to test the wrapper class to make sure that it does actually create/update system environment variables, but you only need to do that the once.