ProcessFiles/ProcessFilesTests/ProcessFiles_UnitTests.cs

using NSubstitute;
using ProcessFiles;
using ProcessFiles.Interfaces;
using Xunit;

namespace ProcessFilesTests;

public class ProcessFilesUnitTests
{
    [Fact]
    public void ProcessFileNotExistTest()
    {
        var result = string.Empty;

        var fakeFileSystem = Substitute.For<IFileSystem>();
        fakeFileSystem.File.Exists(Arg.Any<string>()).Returns(false);

        var test = new FileProcessing(fakeFileSystem);
        var errors = test.Process(["./imaginaryFolder/imaginaryTest.txt"], "txt", TestAction);
        Assert.NotEmpty(errors);
        Assert.Empty(result);

        fakeFileSystem.File.Received().Exists(Arg.Any<string>());
        return;

        void TestAction(string value)
        {
            result = value;
        }
    }

    [Fact]
    public void ProcessFileNoExtensionTest()
    {
        var result = string.Empty;

        var fakeFileSystem = Substitute.For<IFileSystem>();
        fakeFileSystem.File.Exists(Arg.Any<string>()).Returns(true);
        fakeFileSystem.Path.GetExtension(Arg.Any<string>()).Returns(string.Empty);

        var test = new FileProcessing(fakeFileSystem);
        var errors = test.Process(["imaginaryNoExtension"], "abc", TestAction);
        Assert.NotEmpty(errors);
        Assert.Empty(result);

        fakeFileSystem.File.Received().Exists(Arg.Any<string>());
        fakeFileSystem.Path.Received().GetExtension(Arg.Any<string>());
        return;

        void TestAction(string value)
        {
            result = value;
        }
    }

    [Fact]
    public void ProcessFileNotMatchExtensionTest()
    {
        var result = string.Empty;

        var fakeFileSystem = Substitute.For<IFileSystem>();
        fakeFileSystem.File.Exists(Arg.Any<string>()).Returns(true);
        fakeFileSystem.Path.GetExtension(Arg.Any<string>()).Returns("def");

        var test = new FileProcessing(fakeFileSystem);
        var errors = test.Process(["imaginaryFile"], "abc", TestAction);
        Assert.NotEmpty(errors);
        Assert.Empty(result);

        fakeFileSystem.File.Received().Exists(Arg.Any<string>());
        fakeFileSystem.Path.Received().GetExtension(Arg.Any<string>());
        return;

        void TestAction(string value)
        {
            result = value;
        }
    }

    [Fact]
    public void ProcessFileTest()
    {
        var result = string.Empty;

        var fakeFileSystem = Substitute.For<IFileSystem>();
        fakeFileSystem.File.Exists(Arg.Any<string>()).Returns(true);
        fakeFileSystem.Path.GetExtension(Arg.Any<string>()).Returns("txt");

        const string expectedValue = "imaginary.txt";
        var test = new FileProcessing(fakeFileSystem);
        var errors = test.Process([expectedValue], "txt", TestAction);
        Assert.Empty(errors);
        Assert.Equal(expectedValue, result);

        fakeFileSystem.File.Received().Exists(Arg.Any<string>());
        fakeFileSystem.Path.Received().GetExtension(Arg.Any<string>());
        return;

        void TestAction(string value)
        {
            result = value;
        }
    }
}