test(examples): add example program integration tests

Tests/KiteCoreTests/ExampleTests.swift

@@ -0,0 +1,66 @@
+import XCTest
+@testable import KiteCore
+
+final class ExampleTests: XCTestCase {
+    private func examplesDirectory() -> URL {
+        URL(fileURLWithPath: #filePath)
+            .deletingLastPathComponent()
+            .deletingLastPathComponent()
+            .deletingLastPathComponent()
+            .appendingPathComponent("examples")
+    }
+
+    private func runExample(_ name: String) throws -> String {
+        let url = examplesDirectory().appendingPathComponent(name)
+        let source = try String(contentsOf: url, encoding: .utf8)
+        let interp = Interpreter()
+        var captured = ""
+        interp.output = { captured += $0 }
+        try interp.evalString(source)
+        return captured
+    }
+
+    func testFibExample() throws {
+        XCTAssertEqual(try runExample("fib.scm"), "fib 10 = 55\nfib 20 = 6765\nfib 25 = 75025\n")
+    }
+
+    func testFactorialExample() throws {
+        XCTAssertEqual(try runExample("factorial.scm"), "10! = 3628800\n20! = 2432902008176640000\n")
+    }
+
+    func testMapsExample() throws {
+        let expected = """
+        squares: (1 4 9 16 25)
+        odds: (1 3 5 7)
+        sum via fold: 55
+        zip-add: (11 22 33)
+        for-each: abcd
+        append+reverse: (6 5 4 3 2 1)
+
+        """
+        XCTAssertEqual(try runExample("maps.scm"), expected)
+    }
+
+    func testCallCCExample() throws {
+        let expected = """
+        product 1..5 = 120
+        product with a zero = 0
+        reentry sum 1..5 = 15
+
+        """
+        XCTAssertEqual(try runExample("callcc.scm"), expected)
+    }
+
+    func testMacrosExample() throws {
+        let expected = """
+        swap x y -> (2 1)
+        swap tmp other -> (20 10)
+        my-list -> (1 2 3 4 5)
+        my-or -> 7
+        when fired
+        unless fired
+
+        """
+        XCTAssertEqual(try runExample("macros.scm"), expected)
+    }
+}