test(e2e): add end-to-end program tests

src/test/kotlin/lumen/EndToEndTest.kt

@@ -0,0 +1,106 @@
+package lumen
+
+import java.io.File
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+class EndToEndTest {
+    private fun exampleFile(name: String): File {
+        val candidates = listOf(File("examples/$name"), File("../examples/$name"))
+        return candidates.firstOrNull { it.exists() } ?: error("example not found: $name")
+    }
+
+    private fun runExample(name: String): String = Lumen.runToString(exampleFile(name).readText())
+
+    private fun runFileExample(name: String): String {
+        val buffer = StringBuilder()
+        Lumen.runFile(exampleFile(name), buffer)
+        return buffer.toString()
+    }
+
+    @Test
+    fun fibonacciExample() {
+        val expected = buildString {
+            val values = listOf(0, 1, 1, 2, 3, 5, 8, 13, 21, 34)
+            values.forEachIndexed { index, value -> append("fib($index) = $value\n") }
+        }
+        assertEquals(expected, runExample("fib.lumen"))
+    }
+
+    @Test
+    fun fizzBuzzExample() {
+        val expected = buildString {
+            for (n in 1..15) {
+                when {
+                    n % 15 == 0 -> append("FizzBuzz\n")
+                    n % 3 == 0 -> append("Fizz\n")
+                    n % 5 == 0 -> append("Buzz\n")
+                    else -> append("$n\n")
+                }
+            }
+        }
+        assertEquals(expected, runExample("fizzbuzz.lumen"))
+    }
+
+    @Test
+    fun quicksortExample() {
+        val expected = "input:  [5, 3, 8, 1, 9, 2, 7, 4, 6, 0]\nsorted: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]\n"
+        assertEquals(expected, runExample("sort.lumen"))
+    }
+
+    @Test
+    fun closuresExample() {
+        val expected = buildString {
+            append("counter: 1 2 3\n")
+            append("add10(5) = 15\n")
+            append("add100(5) = 105\n")
+            append("doubled: [2, 4, 6, 8, 10]\n")
+            append("evens: [2, 4]\n")
+            append("sum: 15\n")
+        }
+        assertEquals(expected, runExample("closures.lumen"))
+    }
+
+    @Test
+    fun stdlibDemoExample() {
+        val output = runExample("stdlib_demo.lumen")
+        assertTrue(output.contains("sorted:    [1, 2, 3, 5, 8, 9]"), output)
+        assertTrue(output.contains("entries:   [[\"alice\", 90], [\"bob\", 75]]"), output)
+        assertTrue(output.contains("all assertions passed"), output)
+    }
+
+    @Test
+    fun calculatorExampleUsesImportAndStdlib() {
+        val expected = buildString {
+            append("3 4 + 5 * 2 - = 33\n")
+            append("2 3 4 * + = 14\n")
+            append("10 2 / 3 - = 2\n")
+            append("6! = 720\n")
+            append("gcd(48, 36) = 12\n")
+            append("calc checks passed\n")
+        }
+        assertEquals(expected, runFileExample("calc.lumen"))
+    }
+
+    @Test
+    fun csvExampleUsesImportAndStdlib() {
+        val expected = buildString {
+            append("columns: name | score\n")
+            append("Alice scored 90\n")
+            append("Bob scored 75\n")
+            append("Carol scored 88\n")
+            append("total: 253\n")
+            append("best:  90\n")
+            append("csv checks passed\n")
+        }
+        assertEquals(expected, runFileExample("csv.lumen"))
+    }
+
+    @Test
+    fun allExampleFilesExist() {
+        listOf("fib.lumen", "fizzbuzz.lumen", "sort.lumen", "closures.lumen").forEach {
+            assertTrue(runExample(it).isNotEmpty(), "example $it produced no output")
+        }
+    }
+}