add tests for CodingAlphabet ctor behavior

Author: ssg

test/CodingAlphabetTest.cs

@@ -0,0 +1,46 @@
+/*
+     Copyright 2014-2025 Sedat Kapanoglu
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+using System;
+using NUnit.Framework;
+using SimpleBase;
+
+namespace SimpleBaseTest;
+
+[TestFixture]
+class CodingAlphabetTest
+{
+    class DummyAlphabet(string alphabet) : CodingAlphabet(10, alphabet, caseInsensitive: true)
+    {
+    }
+
+    [Test]
+    public void Ctor_WithBothCasesOfLettersAndCaseInsensitive_ShouldThrow()
+    {
+        Assert.Throws<ArgumentException>(() => new DummyAlphabet("01234567Aa"));
+    }
+
+    [Test]
+    public void Ctor_LengthAndAlphabetLengthMismatch_ShouldThrow()
+    {
+        Assert.Throws<ArgumentException>(() => new DummyAlphabet("01234567a"));
+    }
+
+    [Test]
+    public void Ctor_ProperArguments_ShouldNotThrow()
+    {
+        Assert.DoesNotThrow(() => new DummyAlphabet("01234567ab"));
+    }
+}