Added ABS function support, reorganized built-in function tests.

Author: RyanLamansky

SqlServerSimulator.Tests/BuiltInFunctionTests.cs

@@ -7,7 +7,6 @@ namespace SqlServerSimulator;
 [TestClass]
 public sealed class BuiltInFunctionTests
 {
-
     [TestMethod]
     public void UnrecognizedBuiltInFunction()
     {
@@ -16,12 +15,24 @@ public void UnrecognizedBuiltInFunction()
     }
 
     [TestMethod]
-    public void DataLengthOfNull() => IsInstanceOfType<DBNull>(ExecuteScalar("select datalength(null)"));
-
-    [TestMethod]
-    [DataRow("1", 4)]
-    public void DataLength(string input, object? output) => AreEqual(output, ExecuteScalar($"select datalength({input})"));
+    [DataRow("abs")]
+    [DataRow("datalength")]
+    public void NullPassThrough(string function)
+    {
+        AreEqual(function.ToLowerInvariant(), function);
+        _ = IsInstanceOfType<DBNull>(ExecuteScalar($"select {function}(null)"));
+        _ = IsInstanceOfType<DBNull>(ExecuteScalar($"select {function.ToUpperInvariant()}(null)"));
+    }
 
     [TestMethod]
-    public void DataLengthAllCaps() => AreEqual(4, ExecuteScalar<int>("select DATALENGTH(1)"));
+    [DataRow("datalength", "1", 4)]
+    [DataRow("abs", "1", 1)]
+    [DataRow("abs", "0", 0)]
+    [DataRow("abs", "-1", 1)]
+    public void BuiltInFunction(string function, string input, object output)
+    {
+        AreEqual(function.ToLowerInvariant(), function);
+        AreEqual(output, ExecuteScalar($"select {function}({input})"));
+        AreEqual(output, ExecuteScalar($"select {function.ToUpperInvariant()}({input})"));
+    }
 }

SqlServerSimulator/Parser/Expression.cs

@@ -141,7 +141,8 @@ public static Expression Parse(Simulation simulation, IEnumerator<Token> tokens,
     private delegate Expression FunctionResolver(Simulation simulation, IEnumerator<Token> tokens, ref Token? token, Func<string, object?> getVariableValue);
 
     private static readonly FrozenDictionary<string, FunctionResolver> BuiltInFunctions = FrozenDictionary.Create<string, FunctionResolver>(Collation.Default, [
-        new("datalength", (simulation, tokens, ref token, getVariableValue) => new DataLength(Expression.Parse(simulation, tokens, ref token, getVariableValue)))
+        new("datalength", (simulation, tokens, ref token, getVariableValue) => new DataLength(Expression.Parse(simulation, tokens, ref token, getVariableValue))),
+        new("abs", (simulation, tokens, ref token, getVariableValue) => new AbsoluteValue(Expression.Parse(simulation, tokens, ref token, getVariableValue))),
         ]);
 
     private sealed class NamedExpression(Expression expression, string name) : Expression
@@ -281,6 +282,22 @@ public sealed class DataLength(Expression source) : Expression
 
 #if DEBUG
         public override string ToString() => $"DATALENGTH({source})";
+#endif
+    }
+
+    public sealed class AbsoluteValue(Expression source) : Expression
+    {
+        private readonly Expression source = source;
+
+        public override object? Run(Func<List<string>, object?> getColumnValue) => source.Run(getColumnValue) switch
+        {
+            null => null,
+            int value => Math.Abs(value),
+            _ => throw new NotSupportedException($"Simulation unable to to run DATALENGTH function on the provided expression."),
+        };
+
+#if DEBUG
+        public override string ToString() => $"ABS({source})";
 #endif
     }
 }