diff --git a/Sources/sonyalib/Tests/sonyalibTests/sonyalibTests.swift b/Sources/sonyalib/Tests/sonyalibTests/sonyalibTests.swift
index d4c3b4d..a8c72c6 100644
--- a/Sources/sonyalib/Tests/sonyalibTests/sonyalibTests.swift
+++ b/Sources/sonyalib/Tests/sonyalibTests/sonyalibTests.swift
@@ -42,51 +42,102 @@ import Testing
     #expect(tokens == [.recipe("build"), .command("swift build")])
 }
 
-// MARK: - Parser
-
-@Test func parser_single_recipe_with_command() {
-    let tokens: [Token] = [.recipe("build"), .command("swift build")]
-    let ast = Parser().parse(tokens)
-    #expect(ast != nil)
-    #expect(ast?.rules["build"]?.commands == ["swift build"])
+@Test func lexer_unrecognized_line_produces_error_token() {
+    let tokens = Lexer().tokenize("???bad line")
+    #expect(tokens == [.error(line: "???bad line")])
 }
 
-@Test func parser_recipe_with_dependency() {
+@Test func lexer_multiple_errors_in_multiline() {
+    let input = """
+    build:
+    ???bad
+    !!!also bad
+    """
+    let tokens = Lexer().tokenize(input)
+    #expect(tokens.contains(.error(line: "???bad")))
+    #expect(tokens.contains(.error(line: "!!!also bad")))
+}
+
+// MARK: - Parser
+
+@Test func parser_single_recipe_with_command() throws {
+    let tokens: [Token] = [.recipe("build"), .command("swift build")]
+    let ast = try Parser().parse(tokens).get()
+    #expect(ast.rules["build"]?.commands == ["swift build"])
+}
+
+@Test func parser_recipe_with_dependency() throws {
     let tokens: [Token] = [
         .recipe("test"), .dependency("build"),
         .command("swift test")
     ]
-    let ast = Parser().parse(tokens)
-    #expect(ast?.rules["test"]?.dependencies == ["build"])
-    #expect(ast?.rules["test"]?.commands == ["swift test"])
+    let ast = try Parser().parse(tokens).get()
+    #expect(ast.rules["test"]?.dependencies == ["build"])
+    #expect(ast.rules["test"]?.commands == ["swift test"])
 }
 
-@Test func parser_variable_is_stored() {
+@Test func parser_variable_is_stored() throws {
     let tokens: [Token] = [.variable(name: "CC", value: "clang")]
-    let ast = Parser().parse(tokens)
-    #expect(ast?.vars["CC"] == "clang")
+    let ast = try Parser().parse(tokens).get()
+    #expect(ast.vars["CC"] == "clang")
 }
 
-@Test func parser_multiple_recipes() {
+@Test func parser_multiple_recipes() throws {
     let tokens: [Token] = [
         .recipe("build"), .command("swift build"),
         .newline,
         .recipe("test"), .command("swift test"),
     ]
-    let ast = Parser().parse(tokens)
-    #expect(ast?.rules["build"]?.commands == ["swift build"])
-    #expect(ast?.rules["test"]?.commands == ["swift test"])
+    let ast = try Parser().parse(tokens).get()
+    #expect(ast.rules["build"]?.commands == ["swift build"])
+    #expect(ast.rules["test"]?.commands == ["swift test"])
 }
 
-@Test func parser_variable_before_recipe_flushes_context() {
-    // A variable declaration after a recipe must flush the current recipe first.
+@Test func parser_variable_before_recipe_flushes_context() throws {
     let tokens: [Token] = [
         .recipe("build"), .command("swift build"),
         .variable(name: "X", value: "1"),
     ]
-    let ast = Parser().parse(tokens)
-    #expect(ast?.rules["build"]?.commands == ["swift build"])
-    #expect(ast?.vars["X"] == "1")
+    let ast = try Parser().parse(tokens).get()
+    #expect(ast.rules["build"]?.commands == ["swift build"])
+    #expect(ast.vars["X"] == "1")
+}
+
+// MARK: - Parser error handling
+
+@Test func parser_single_error_token_returns_failure() {
+    let tokens: [Token] = [.error(line: "???bad")]
+    let result = Parser().parse(tokens)
+    guard case .failure(let err) = result else {
+        Issue.record("expected failure, got success")
+        return
+    }
+    #expect(err.errorLines == ["???bad"])
+}
+
+@Test func parser_multiple_error_tokens_collected() {
+    let tokens: [Token] = [
+        .error(line: "???bad"),
+        .recipe("build"), .command("swift build"),
+        .error(line: "!!!also bad"),
+    ]
+    let result = Parser().parse(tokens)
+    guard case .failure(let err) = result else {
+        Issue.record("expected failure, got success")
+        return
+    }
+    #expect(err.errorLines.count == 2)
+    #expect(err.errorLines.contains("???bad"))
+    #expect(err.errorLines.contains("!!!also bad"))
+}
+
+@Test func parser_no_error_tokens_returns_success() {
+    let tokens: [Token] = [.recipe("build"), .command("swift build")]
+    let result = Parser().parse(tokens)
+    guard case .success = result else {
+        Issue.record("expected success, got failure")
+        return
+    }
 }
 
 // MARK: - Variable resolution