Lexer testing infra

Cargo.toml

@@ -3,4 +3,6 @@ name = "libsyntax2"
 version = "0.1.0"
 authors = ["Aleksey Kladov <aleksey.kladov@gmail.com>"]
 
-[dependencies]
+[dev-dependencies]
+file = "1.1.1"
+difference = "1.0.0"

tests/data/lexer/0001_hello.rs

@@ -0,0 +1 @@
+hello world

tests/data/lexer/0001_hello.txt

@@ -0,0 +1,3 @@
+IDENT 5
+WHITESPACE 1
+IDENT 5

tests/lexer.rs

@@ -0,0 +1,55 @@
+extern crate file;
+#[macro_use(assert_diff)]
+extern crate difference;
+
+use std::path::{PathBuf, Path};
+use std::fs::read_dir;
+
+#[test]
+fn lexer_tests() {
+    for test_case in lexer_test_cases() {
+        lexer_test_case(&test_case);
+    }
+}
+
+fn lexer_test_dir() -> PathBuf {
+    let dir = env!("CARGO_MANIFEST_DIR");
+    PathBuf::from(dir).join("tests/data/lexer")
+}
+
+fn lexer_test_cases() -> Vec<PathBuf> {
+    let mut acc = Vec::new();
+    let dir = lexer_test_dir();
+    for file in read_dir(&dir).unwrap() {
+        let file = file.unwrap();
+        let path = file.path();
+        if path.extension().unwrap_or_default() == "rs" {
+            acc.push(path);
+        }
+    }
+    acc
+}
+
+fn lexer_test_case(path: &Path) {
+    let actual = {
+        let text = file::get_text(path).unwrap();
+        let tokens = tokenize(&text);
+        dump_tokens(&tokens)
+    };
+    let expected = file::get_text(&path.with_extension("txt")).unwrap();
+
+    assert_diff!(
+        expected.as_str(),
+        actual.as_str(),
+        "\n",
+        0
+    )
+}
+
+fn tokenize(text: &str) -> Vec<()> {
+    Vec::new()
+}
+
+fn dump_tokens(tokens: &[()]) -> String {
+    "IDENT 5\nKEYWORD 1\nIDENT 5\n".to_string()
+}