Add new tests for console, function, system, variable, and code flow statements

YesNt.Interpreter.Tests/SystemStatementsTests.cs

@@ -0,0 +1,48 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+using System.Collections.Generic;
+
+namespace YesNt.Interpreter.Tests;
+
+[TestClass]
+public class SystemStatementsTests
+{
+    [TestMethod]
+    public void ExecWithArgsRunsProcessTest()
+    {
+        List<string> lines =
+        [
+            "exec cmd with /c,echo yesnt",
+            "let exitCode = %out",
+            "${exitCode}"
+        ];
+
+        YesNtAssert.IsLastLineEqual(lines, "0");
+    }
+
+    [TestMethod]
+    public void ExecWithInStackArgsRunsProcessTest()
+    {
+        List<string> lines =
+        [
+            "push_in /c",
+            "push_in echo yesnt",
+            "exec cmd",
+            "let exitCode = %out",
+            "${exitCode}"
+        ];
+
+        YesNtAssert.IsLastLineEqual(lines, "0");
+    }
+
+    [TestMethod]
+    public void ExecInvalidProgramFailsTest()
+    {
+        List<string> lines =
+        [
+            "exec does_not_exist_abc_xyz"
+        ];
+
+        YesNtAssert.ContainsTerminationMessage(lines, "Failed to start \"does_not_exist_abc_xyz\"");
+    }
+}