GoogleTest

GoogleTest クレートにより、マッチャーを使用した柔軟なテスト アサーションが可能になります。

use googletest::prelude::*;

#[googletest::test]
fn test_elements_are() {
    let value = vec!["foo", "bar", "baz"];
    expect_that!(value, elements_are!(eq(&"foo"), lt(&"xyz"), starts_with("b")));
}

最後の要素を "!" に変更すると、テストは失敗し、エラー箇所を示す構造化されたエラー メッセージが表示されます。

---- test_elements_are stdout ----
Value of: value
Expected: has elements:
  0. is equal to "foo"
  1. is less than "xyz"
  2. starts with prefix "!"
Actual: ["foo", "bar", "baz"],
  where element #2 is "baz", which does not start with "!"
  at src/testing/googletest.rs:6:5
Error: See failure output above

Speaker Notes

 This slide should take about 5 minutes.

  • GoogleTest は Rust プレイグラウンドの一部ではないため、この例はローカル環境で実行する必要があります。cargo add googletest を使用して、既存の Cargo プロジェクトにすばやく追加します。

  • use googletest::prelude::*; 行は、一般的に使用されるマクロと型をインポートします。

  • This just scratches the surface, there are many builtin matchers. Consider going through the first chapter of “Advanced testing for Rust applications”, a self-guided Rust course: it provides a guided introduction to the library, with exercises to help you get comfortable with googletest macros, its matchers and its overall philosophy.

  • A particularly nice feature is that mismatches in multi-line strings are shown as a diff:

#[test]
fn test_multiline_string_diff() {
    let haiku = "Memory safety found,\n\
                 Rust's strong typing guides the way,\n\
                 Secure code you'll write.";
    assert_that!(
        haiku,
        eq("Memory safety found,\n\
            Rust's silly humor guides the way,\n\
            Secure code you'll write.")
    );
}

これにより、差分が色分けされます（ここでは色分けされていません）。

    Value of: haiku
Expected: is equal to "Memory safety found,\nRust's silly humor guides the way,\nSecure code you'll write."
Actual: "Memory safety found,\nRust's strong typing guides the way,\nSecure code you'll write.",
  which isn't equal to "Memory safety found,\nRust's silly humor guides the way,\nSecure code you'll write."
Difference(-actual / +expected):
 Memory safety found,
-Rust's strong typing guides the way,
+Rust's silly humor guides the way,
 Secure code you'll write.
  at src/testing/googletest.rs:17:5