feat: expand integration test coverage for edge cases

tests/edge_cases.rs

@@ -0,0 +1,52 @@
+mod harness;
+
+use harness::ShellTest;
+
+// ============================================================================
+// Edge Cases
+//
+// This file covers scenarios not already exercised in tests/builtin.rs or
+// tests/repl.rs. Scenarios that duplicate existing coverage (cd-nonexistent,
+// cd-to-file, exit 42, type system executable, sequential echo, empty script)
+// live in those files.
+// ============================================================================
+
+/// type echo specifically identifies echo as a shell builtin (not a PATH binary).
+/// This is distinct from test_type_identifies_builtin in builtin.rs, which uses
+/// `type exit`; it validates that a command with a common system binary namesake
+/// is still correctly identified as a builtin by ferrish.
+#[test]
+fn test_type_builtin_echo_shows_builtin() {
+    let result = ShellTest::new()
+        .with_isolated_home()
+        .script("type echo")
+        .run();
+
+    let output = result.output();
+    assert!(
+        output.contains("echo"),
+        "type echo should mention 'echo', got: {}",
+        output
+    );
+    assert!(
+        output.contains("builtin"),
+        "type echo should identify echo as a builtin, got: {}",
+        output
+    );
+}
+
+/// Whitespace-only lines (spaces and tabs) do not produce errors and the shell
+/// continues processing subsequent commands.
+#[test]
+fn test_whitespace_only_lines_no_error() {
+    let result = ShellTest::new()
+        .script("   \n\t\n  \t  \necho alive")
+        .run();
+
+    assert!(
+        result.error().is_empty(),
+        "Whitespace-only lines should not produce errors, got: {}",
+        result.error()
+    );
+    result.assert_output_contains("alive");
+}