tests: Add NUnit suite for InputInterpreter.Interpret covering arithmetic, comparisons, variables, := binding, arrays, soft errors, and timing

Adds InputInterpreterTests with:

- Arithmetic cases including precedence, hex/binary, exponent.
- Comparisons yielding numeric booleans.
- Variable assignment (::) and persistence across calls; unknown variable soft error.
- Expression binding (:=) re-evaluated at use-time; invalid expression soft error.
- Array assignment (->) and indexing; out-of-range and index-expression scenarios.
- String literal used as expression soft error.
- Divide-by-zero soft error (no thrown exception).
- LastExecutionTime measured across calls.

Each test asserts both the return value and NumericValue/StringValue for consistency.

src/tests/InputInterpreterTests.cs

@@ -1,16 +1,139 @@
-namespace tests
+using System.Globalization;
+using csmic;
+
+namespace tests;
+
+public class InputInterpreterTests
 {
-    public class InputInterpreterTests
-    {
+    private InputInterpreter _interp = null!;
+
     [SetUp]
     public void Setup()
     {
+        CultureInfo.CurrentCulture = CultureInfo.InvariantCulture;
+        _interp = new InputInterpreter();
+    }
+
+    private static void AssertSuccess(decimal result, decimal expected, InputInterpreter interp)
+    {
+        Assert.That(result, Is.EqualTo(expected));
+        Assert.That(interp.NumericValue, Is.EqualTo(expected));
+        Assert.That(interp.StringValue, Is.EqualTo(string.Empty));
+    }
+
+    private static void AssertSoftError(decimal result, InputInterpreter interp)
+    {
+        Assert.That(result, Is.EqualTo(0m));
+        Assert.That(interp.NumericValue, Is.EqualTo(0m));
+        Assert.That(string.IsNullOrEmpty(interp.StringValue), Is.False);
+    }
+
+    [TestCase("2", 2)]
+    [TestCase("-5", -5)]
+    [TestCase("2+3*4", 14)]
+    [TestCase("(2+3)*4", 20)]
+    [TestCase("8/2", 4)]
+    [TestCase("7%4", 3)]
+    [TestCase("2^3", 8)]
+    [TestCase("1e2", 100)]
+    [TestCase("0xFF", 255)]
+    [TestCase("1010b", 10)]
+    public void Arithmetic_Works(string expr, decimal expected)
+    {
+        var result = _interp.Interpret(expr);
+        AssertSuccess(result, expected, _interp);
+    }
+
+    [TestCase("2==2", 1)]
+    [TestCase("2<3", 1)]
+    [TestCase("3<2", 0)]
+    [TestCase("2>=2", 1)]
+    [TestCase("2<=1", 0)]
+    public void Comparisons_YieldBooleanAsNumeric(string expr, decimal expected)
+    {
+        var result = _interp.Interpret(expr);
+        AssertSuccess(result, expected, _interp);
     }
 
     [Test]
-        public void Test1()
+    public void Variables_AssignAndUse_PersistAcrossCalls()
     {
-            Assert.Pass();
+        AssertSuccess(_interp.Interpret("x :: 2"), 2, _interp);
+        AssertSuccess(_interp.Interpret("x+1"), 3, _interp);
+        AssertSuccess(_interp.Interpret("x :: 3"), 3, _interp);
+        AssertSuccess(_interp.Interpret("x+1"), 4, _interp);
     }
+
+    [Test]
+    public void UnknownVariable_ProducesSoftError()
+    {
+        var result = _interp.Interpret("nope + 1");
+        AssertSoftError(result, _interp);
+    }
+
+    [Test]
+    public void ExpressionBinding_EvaluatesAtUseTime()
+    {
+        AssertSuccess(_interp.Interpret("num :: 2"), 2, _interp);
+        AssertSuccess(_interp.Interpret("exp := 1 + num"), 0, _interp); // assignment returns 0
+        AssertSuccess(_interp.Interpret("exp"), 3, _interp);
+
+        AssertSuccess(_interp.Interpret("num :: 3"), 3, _interp);
+        AssertSuccess(_interp.Interpret("exp"), 4, _interp);
+    }
+
+    [Test]
+    public void ExpressionBinding_InvalidExpression_ProducesSoftError()
+    {
+        _interp.Interpret("exp := bad + 1");
+        var result = _interp.Interpret("exp");
+        AssertSoftError(result, _interp);
+    }
+
+    [Test]
+    public void Arrays_AssignAndIndex()
+    {
+        AssertSuccess(_interp.Interpret("arr -> [1,2,3]"), 0, _interp); // array assignment returns 0
+        AssertSuccess(_interp.Interpret("arr[0]"), 1, _interp);
+        AssertSuccess(_interp.Interpret("arr[2]"), 3, _interp);
+    }
+
+    [Test]
+    public void Arrays_OutOfRange_ProducesSoftError()
+    {
+        _interp.Interpret("arr -> [1,2,3]");
+        var result = _interp.Interpret("arr[3]");
+        AssertSoftError(result, _interp);
+    }
+
+    [Test]
+    public void Arrays_IndexExpression_Works()
+    {
+        _interp.Interpret("arr -> [1,2,3]");
+        _interp.Interpret("i :: 1");
+        AssertSuccess(_interp.Interpret("arr[i+1]"), 3, _interp);
+    }
+
+    [Test]
+    public void StringLiteral_Alone_IsError()
+    {
+        var result = _interp.Interpret("\"hi\"");
+        AssertSoftError(result, _interp);
+    }
+
+    [Test]
+    public void DivideByZero_ProducesSoftError()
+    {
+        var result = _interp.Interpret("1/0");
+        AssertSoftError(result, _interp);
+    }
+
+    [Test]
+    public void LastExecutionTime_IsMeasured()
+    {
+        _interp.Interpret("2+2");
+        Assert.That(_interp.LastExecutionTime, Is.GreaterThanOrEqualTo(TimeSpan.Zero));
+        _interp.Interpret("3+3");
+        Assert.That(_interp.LastExecutionTime, Is.GreaterThanOrEqualTo(TimeSpan.Zero));
     }
 }