test(compiler): add compiler tests

src/test/kotlin/lumen/CompilerTest.kt

@@ -0,0 +1,75 @@
+package lumen
+
+import lumen.bytecode.Opcode
+import lumen.runtime.FunctionValue
+import lumen.runtime.IntValue
+import lumen.runtime.StringValue
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertIs
+import kotlin.test.assertTrue
+
+class CompilerTest {
+    @Test
+    fun emitsExactBytecodeForArithmetic() {
+        val script = Lumen.compile("1 + 2")
+        assertEquals(
+            listOf(
+                Opcode.Constant.ordinal, 0,
+                Opcode.Constant.ordinal, 1,
+                Opcode.Add.ordinal,
+                Opcode.Pop.ordinal,
+                Opcode.Nil.ordinal,
+                Opcode.Return.ordinal
+            ),
+            script.chunk.code
+        )
+        assertEquals(listOf<Any>(IntValue(1), IntValue(2)), script.chunk.constants)
+    }
+
+    @Test
+    fun emitsNegateForUnaryMinus() {
+        val script = Lumen.compile("-5")
+        assertEquals(
+            listOf(
+                Opcode.Constant.ordinal, 0,
+                Opcode.Negate.ordinal,
+                Opcode.Pop.ordinal,
+                Opcode.Nil.ordinal,
+                Opcode.Return.ordinal
+            ),
+            script.chunk.code
+        )
+    }
+
+    @Test
+    fun globalDeclarationEmitsDefineGlobal() {
+        val script = Lumen.compile("let x = 5")
+        assertTrue(script.chunk.code.contains(Opcode.DefineGlobal.ordinal))
+        assertTrue(script.chunk.constants.contains(StringValue("x")))
+        assertTrue(script.chunk.constants.contains(IntValue(5)))
+    }
+
+    @Test
+    fun functionCompilesToNestedFunctionConstant() {
+        val script = Lumen.compile("fn f() { return 42 }")
+        assertTrue(script.chunk.code.contains(Opcode.Closure.ordinal))
+        val function = assertIs<FunctionValue>(script.chunk.constants.first { it is FunctionValue })
+        assertEquals("f", function.name)
+        assertEquals(0, function.arity)
+        assertTrue(function.chunk.constants.contains(IntValue(42)))
+    }
+
+    @Test
+    fun shortCircuitAndEmitsJumpIfFalse() {
+        val script = Lumen.compile("true and false")
+        assertTrue(script.chunk.code.contains(Opcode.JumpIfFalse.ordinal))
+    }
+
+    @Test
+    fun forLoopEmitsIteratorOpcodes() {
+        val script = Lumen.compile("for (i in items) { print(i) }")
+        assertTrue(script.chunk.code.contains(Opcode.GetIter.ordinal))
+        assertTrue(script.chunk.code.contains(Opcode.ForIter.ordinal))
+    }
+}