test(vm): add method and stdlib tests

src/test/kotlin/lumen/MethodTest.kt

@@ -0,0 +1,59 @@
+package lumen
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+
+class MethodTest {
+    private fun output(source: String) = Lumen.runToString(source)
+
+    @Test
+    fun methodOnLiteralReceiver() {
+        assertEquals("ABC\n", output("println(\"abc\".upper())"))
+        assertEquals("[1, 2, 3]\n", output("println([3, 2, 1].sort())"))
+    }
+
+    @Test
+    fun chainedMethodCalls() {
+        assertEquals("CBA\n", output("println(\"abc\".upper().chars().reverse().join(\"\"))"))
+    }
+
+    @Test
+    fun methodMutatesReceiverInPlace() {
+        val program = """
+            let xs = [1, 2]
+            xs.push(3)
+            println(xs)
+            println(xs.len())
+        """.trimIndent()
+        assertEquals("[1, 2, 3]\n3\n", output(program))
+    }
+
+    @Test
+    fun dispatchDependsOnReceiverType() {
+        assertEquals("true\n", output("println([1, 2, 3].contains(2))"))
+        assertEquals("true\n", output("println(\"abc\".contains(\"b\"))"))
+    }
+
+    @Test
+    fun higherOrderMethods() {
+        assertEquals("[2, 4, 6]\n", output("println([1, 2, 3].map(fn(x) { return x * 2 }))"))
+        assertEquals("[2, 4]\n", output("println([1, 2, 3, 4].filter(fn(x) { return x % 2 == 0 }))"))
+        assertEquals("10\n", output("println([1, 2, 3, 4].reduce(fn(a, b) { return a + b }, 0))"))
+    }
+
+    @Test
+    fun unknownMethodFails() {
+        assertFailsWith<RuntimeError> { output("println([1].frobnicate())") }
+    }
+
+    @Test
+    fun methodWrongArityFails() {
+        assertFailsWith<RuntimeError> { output("println(\"a\".upper(1))") }
+    }
+
+    @Test
+    fun methodOnWrongTypeFails() {
+        assertFailsWith<RuntimeError> { output("println(42.upper())") }
+    }
+}