Add unit tests (#887)

* Add unit test project

* Add initial unit tests

TwitchDownloaderTests/GlobalUsings.cs

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+global using Xunit;

TwitchDownloaderTests/ReadOnlySpanTryReplaceNonEscapedTests.cs

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+using TwitchDownloaderCore.Extensions;
+
+namespace TwitchDownloaderTests
+{
+    // ReSharper disable StringLiteralTypo
+    public class ReadOnlySpanTryReplaceNonEscapedTests
+    {
+        [Fact]
+        public void ReturnsFalse_WhenDestinationTooShort()
+        {
+            ReadOnlySpan<char> str = @"SORRY FOR TRAFFIC NaM";
+            var destination = Array.Empty<char>();
+
+            var success = str.TryReplaceNonEscaped(destination, 'r', 'w');
+
+            Assert.False(success);
+        }
+
+        [Fact]
+        public void MatchesOriginalString_WhenOldCharNotFound()
+        {
+            ReadOnlySpan<char> str = @"SORRY FOR TRAFFIC NaM";
+            var destination = new char[str.Length];
+            const string EXPECTED = @"SORRY FOR TRAFFIC NaM";
+
+            var success = str.TryReplaceNonEscaped(destination, 'r', 'w');
+
+            Assert.True(success);
+            Assert.Equal(EXPECTED.AsSpan(), destination);
+        }
+
+        [Fact]
+        public void CorrectlyEscapeCharsPrependedByBackslash()
+        {
+            ReadOnlySpan<char> str = @"SO\RRY FO\R TRAFFIC NaM";
+            var destination = new char[str.Length];
+            const string EXPECTED = @"SO\RWY FO\R TWAFFIC NaM";
+
+            var success = str.TryReplaceNonEscaped(destination, 'R', 'W');
+
+            Assert.True(success);
+            Assert.Equal(EXPECTED.AsSpan(), destination);
+        }
+
+        [Fact]
+        public void CorrectlyEscapeSingleCharsContainedWithinQuotes()
+        {
+            ReadOnlySpan<char> str = "SO\"R\"RY FO'R' TRAFFIC NaM";
+            var destination = new char[str.Length];
+            const string EXPECTED = "SO\"R\"WY FO'R' TWAFFIC NaM";
+
+            var success = str.TryReplaceNonEscaped(destination, 'R', 'W');
+
+            Assert.True(success);
+            Assert.Equal(EXPECTED.AsSpan(), destination);
+        }
+
+        [Fact]
+        public void CorrectlyEscapeManyCharsContainedWithinQuotes()
+        {
+            ReadOnlySpan<char> str = "SORRY \"FOR\" 'TRAFFIC' NaM";
+            var destination = new char[str.Length];
+            const string EXPECTED = "SOWWY \"FOR\" 'TRAFFIC' NaM";
+
+            var success = str.TryReplaceNonEscaped(destination, 'R', 'W');
+
+            Assert.True(success);
+            Assert.Equal(EXPECTED.AsSpan(), destination);
+        }
+
+        [Fact]
+        public void CorrectlyEscapesEndQuotesPrependedByBackslashes()
+        {
+            ReadOnlySpan<char> str = @"'It\'s finally over.' It truly is over.";
+            var destination = new char[str.Length];
+            const string EXPECTED = @"'It\'s finally over.' It twuly is ovew.";
+
+            var success = str.TryReplaceNonEscaped(destination, 'r', 'w');
+
+            Assert.True(success);
+            Assert.Equal(EXPECTED.AsSpan(), destination);
+        }
+
+        [Fact]
+        public void DoesNotEscapeDifferingQuotes()
+        {
+            ReadOnlySpan<char> str = "\"SORRY FOR TRAFFIC NaM.'";
+            var destination = new char[str.Length];
+
+            var success = str.TryReplaceNonEscaped(destination, 'R', 'W');
+
+            Assert.False(success);
+        }
+    }
+}

TwitchDownloaderTests/StringReplaceAnyTests.cs

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+using TwitchDownloaderCore.Extensions;
+
+namespace TwitchDownloaderTests
+{
+    // ReSharper disable StringLiteralTypo
+    public class StringReplaceAnyTests
+    {
+        [Fact]
+        public void MatchesMultipleStringReplaceUses()
+        {
+            const string STRING = "SORRY FOR TRAFFIC NaM.";
+            const string OLD_CHARS = "FRM";
+            const char NEW_CHAR = 'L';
+
+            var replaceResult1 = STRING.Replace(OLD_CHARS[0], NEW_CHAR);
+            var replaceResult2 = replaceResult1.Replace(OLD_CHARS[1], NEW_CHAR);
+            var replaceResult3 = replaceResult2.Replace(OLD_CHARS[2], NEW_CHAR);
+
+            var replaceAnyResult = replaceResult2.ReplaceAny(OLD_CHARS, NEW_CHAR);
+
+            Assert.Equal(replaceResult3, replaceAnyResult);
+        }
+
+        [Fact]
+        public void CorrectlyReplacesAnyCharacter()
+        {
+            const string STRING = "SORRY FOR TRAFFIC NaM.";
+            const string OLD_CHARS = "FRM";
+            const char NEW_CHAR = 'L';
+            const string EXPECTED = "SOLLY LOL TLALLIC NaL.";
+
+            var result = STRING.ReplaceAny(OLD_CHARS, NEW_CHAR);
+
+            Assert.Equal(EXPECTED, result);
+        }
+
+        [Fact]
+        public void ReturnsOriginalString_WhenEmpty()
+        {
+            const string STRING = "";
+            const string OLD_CHARS = "";
+            const char NEW_CHAR = 'L';
+
+            var result = STRING.ReplaceAny(OLD_CHARS, NEW_CHAR);
+
+            Assert.Same(STRING, result);
+        }
+
+        [Fact]
+        public void ReturnsOriginalString_WhenOldCharsNotPresent()
+        {
+            const string STRING = "SORRY FOR TRAFFIC NaM.";
+            const string OLD_CHARS = "PogU";
+            const char NEW_CHAR = 'L';
+
+            var result = STRING.ReplaceAny(OLD_CHARS, NEW_CHAR);
+
+            Assert.Same(STRING, result);
+        }
+    }
+}