EnvironmentAbstractions

The EnvironmentAbstractions package provides an interface, IEnvironmentProvider, that can be used as a layer of abstraction for code to be easier to mock for unit testing.

IEnvironmentProvider

The IEnvironmentProvider interfaces supports the following members:

public interface IEnvironmentProvider : IEnvironmentVariableProvider { string CommandLine { get; } string CurrentDirectory { get; set; } int CurrentManagedThreadId { get; } int ExitCode { get; } bool HasShutdownStarted { get; } bool Is64BitOperatingSystem { get; } bool Is64BitProcess { get; } string MachineName { get; } string NewLine { get; } OperatingSystem OSVersion { get; } #if NET5_0_OR_GREATER int ProcessId { get; } #endif int ProcessorCount { get; } #if NET6_0_OR_GREATER string? ProcessPath { get; } #endif string StackTrace { get; } string SystemDirectory { get; } int SystemPageSize { get; } int TickCount { get; } #if NETCOREAPP3_1_OR_GREATER long TickCount64 { get; } #endif string UserDomainName { get; } bool UserInteractive { get; } string UserName { get; } Version Version { get; } long WorkingSet { get; } void Exit(int exitCode); void FailFast(string? message); void FailFast(string? message, Exception? exception); string? ExpandEnvironmentVariables(string name); string? GetEnvironmentVariable(string name, EnvironmentVariableTarget target); string? GetEnvironmentVariable(string name); IReadOnlyDictionary<string, string> GetEnvironmentVariables(); IReadOnlyDictionary<string, string> GetEnvironmentVariables(EnvironmentVariableTarget target); string[] GetCommandLineArgs(); string GetFolderPath(Environment.SpecialFolder folder); string GetFolderPath(Environment.SpecialFolder folder, Environment.SpecialFolderOption option); string[] GetLogicalDrives(); void SetEnvironmentVariable(string name, string? value); void SetEnvironmentVariable(string name, string? value, EnvironmentVariableTarget target); }

IEnvironmentVariableProvider

The IEnvironmentVariableProvider interface is just for abstracting away access to environment variables and supports the following methods:

public interface IEnvironmentVariableProvider { string? ExpandEnvironmentVariables(string name); string? GetEnvironmentVariable(string name, EnvironmentVariableTarget target); string? GetEnvironmentVariable(string name); IReadOnlyDictionary<string, string> GetEnvironmentVariables(); IReadOnlyDictionary<string, string> GetEnvironmentVariables(EnvironmentVariableTarget target); void SetEnvironmentVariable(string name, string? value); void SetEnvironmentVariable(string name, string? value, EnvironmentVariableTarget target); }

Examples

The example below shows how to use IEnvironmentProvider in a class to access the environment. You should have two constructors: one that does default logic and another that accepts an IEnvironmentProvider instance. The constructor that accepts an IEnvironmentProvider can be internal so it can only be called by unit tests.

public class MyClass { private readonly IEnvironmentProvider environmentProvider; /// <summary> /// Internal constructor only for unit tests which accesses the environment from the specified IEnvironmentProvider. /// </summary> internal MyClass(IEnvironmentProvider environmentProvider) { this.environmentProvider = environmentProvider } /// <summary> /// Initializes a new instance of the MyClass class which accesses the environment directly from the system. /// </summary> public MyClass() : this(SystemEnvironmentProvider.Instance) { } public void SayHello() { // Get the current username from IEnvironmentProvider so that a test can mock the value Console.WriteLine("Hello {0}!", environmentProvider.UserName); } public CustomConfig GetConfiguration() { // Check if the user has set an environment variable to override the default location string customConfigLocation = environmentProvider.GetEnvironmentVariable("CUSTOM_CONFIG"); if (!string.IsNullOrWhitespace(environmentProvider)) { return LoadConfigFromLocation(customConfigLocation); } // Load the configuration from the default location, %UserProfile%\configuration.xml return LoadConfiguationFromLocation(Path.Combine(environmentProvider.GetEnvironmentVariable("USERPROFILE"), "configuration.xml")); } }

Alternatively, you can use the IEnvironmentVariableProvider interface in a class to only abstract away access to environment variables. Like the example above, you should have two constructors: one that does default logic and another that accepts an IEnvironmentVariableProvider instance. The constructor that accepts an IEnvironmentVariableProvider can be internal so it can only be called by unit tests.

public class MyClass { private readonly IEnvironmentVariableProvider environmentVariableProvider; /// <summary> /// Internal constructor only for unit tests which reads environment variables from the specified IEnvironmentVariableProvider. /// </summary> internal MyClass(IEnvironmentVariableProvider environmentVariableProvider) { this.environmentVariableProvider = environmentVariableProvider } /// <summary> /// Initializes a new instance of the MyClass class which reads environment variables directly from the system. /// </summary> public MyClass() : this(SystemEnvironmentVariableProvider.Instance) { } public CustomConfig GetConfiguration() { // Check if the user has set an environment variable to override the default location string customConfigLocation = environmentVariableProvider.GetEnvironmentVariable("CUSTOM_CONFIG"); if (!string.IsNullOrWhitespace(environmentVariableProvider)) { return LoadConfigFromLocation(customConfigLocation); } // Load the configuration from the default location, %UserProfile%\configuration.xml return LoadConfiguationFromLocation(Path.Combine(environmentVariableProvider.GetEnvironmentVariable("USERPROFILE"), "configuration.xml")); } }

Unit tests can then use the MockEnvironmentProvider or MockEnvironmentVariableProvider class from the EnvironmentAbstractions.TestHelpers package, an existing mocking framework like Moq, or any custom implementation.

MockEnvironmentProvider

[Fact] public void MethodReturnsExpectedValue() { IEnvironmentProvider environmentProvider = new MockEnvironmentProvider { // Initializes this instance to have the UserName property return "UserA" UserName = "UserA", }; // Sets an environment variable value environmentProvider["Variable1"] = "Value1"; MyClass instance = new MyClass(environmentVariableProvider); string actualUsername = instance.GetUserName(); Assert.Equal(actualUsername, "UserA"); }

MockEnvironmentVariableProvider

[Fact] public void MethodReturnsExpectedValue() { IEnvironmentVariableProvider environmentVariableProvider = new MockEnvironmentVariableProvider environmentVariableProvider["Variable1"] = "Value1"; MyClass instance = new MyClass(environmentVariableProvider); string value = instance.Method(); }

Preventing usage of System.Environment

If you want to use IEnvironmentProvider or IEnvironmentVariableProvider exclusively in your repository, you can reference the EnvironmentAbstractions.BannedApiAnalyzer package which uses the Microsoft.CodeAnalysis.BannedApiAnalyzers Roslyn analyzer to prevent code from accessing the System.Environment APIs.

Sample project

<Project Sdk="Microsoft.NET.Sdk"> <PropertyGroup> <TargetFramework>netstandard2.0</TargetFramework> </PropertyGroup> <ItemGroup> <PackageReference Include="EnvironmentAbstractions.BannedApiAnalyzer" Version="1.0.0" /> </ItemGroup> </Project>

Sample source code

public static void Main(string[] args) { Console.WriteLine("Hello, {0}!", System.Environment.GetEnvironmentVariable("USERNAME")); }

Sample error

warning RS0030: The symbol 'Environment.GetEnvironmentVariable(string)' is banned in this project: Use IEnvironmentVariableProvider.GetEnvironmentVariable(string) instead.