StringTooLong and tests

src/GuardClauses/GuardAgainstStringLengthExtensions.cs

@@ -36,4 +36,36 @@ public static string StringTooShort(this IGuardClause guardClause,
         }
         return input;
     }
+
+    /// <summary>
+    /// Throws an <see cref="ArgumentException" /> if string <paramref name="input"/> is too long.
+    /// </summary>
+    /// <param name="guardClause"></param>
+    /// <param name="input"></param>
+    /// <param name="maxLength"></param>
+    /// <param name="parameterName"></param>
+    /// <param name="message">Optional. Custom error message</param>
+    /// <returns><paramref name="input" /> if the value is not negative.</returns>
+    /// <exception cref="ArgumentException"></exception>
+#if NETFRAMEWORK || NETSTANDARD2_0
+    public static string StringTooLong(this IGuardClause guardClause,
+        string input,
+        int maxLength,
+        string parameterName,
+        string? message = null)
+#else
+    public static string StringTooLong(this IGuardClause guardClause,
+        string input,
+        int maxLength,
+        [CallerArgumentExpression("input")] string? parameterName = null,
+        string? message = null)
+#endif
+    {
+        Guard.Against.NegativeOrZero(maxLength, nameof(maxLength));
+        if (input.Length > maxLength)
+        {
+            throw new ArgumentException(message ?? $"Input {parameterName} with length {input.Length} is too long. Maxmimum length is {maxLength}.", parameterName);
+        }
+        return input;
+    }
 }

test/GuardClauses.UnitTests/GuardAgainstStringTooLong.cs

@@ -0,0 +1,39 @@
+using System;
+using Ardalis.GuardClauses;
+using Xunit;
+
+namespace GuardClauses.UnitTests;
+
+public class GuardAgainstStringTooLong
+{
+    [Fact]
+    public void DoesNothingGivenNonEmptyString()
+    {
+        Guard.Against.StringTooLong("a", 3, "string");
+        Guard.Against.StringTooLong("abc", 3, "string");
+        Guard.Against.StringTooLong("a", 3, "string");
+        Guard.Against.StringTooLong("a", 3, "string");
+        Guard.Against.StringTooLong("a", 3, "string");
+    }
+
+    [Fact]
+    public void ThrowsGivenNonPositiveMaxLength()
+    {
+        Assert.Throws<ArgumentException>(() => Guard.Against.StringTooLong("a", 0, "string"));
+        Assert.Throws<ArgumentException>(() => Guard.Against.StringTooLong("a", -1, "string"));
+    }
+
+    [Fact]
+    public void ThrowsGivenStringLongerThanMaxLength()
+    {
+        Assert.Throws<ArgumentException>(() => Guard.Against.StringTooLong("abc", 2, "string"));
+    }
+
+    [Fact]
+    public void ReturnsExpectedValueWhenGivenValidString()
+    {
+        var expected = "abc";
+        var actual = Guard.Against.StringTooLong("abc", 3, "string");
+        Assert.Equal(expected, actual);
+    }
+}