GoogleTest

The GoogleTest crate allows for flexible test assertions using matchers:

1. use googletest::prelude::*;

3. #[googletest::test]
4. fn test_elements_are() {
5. let value = vec!["foo", "bar", "baz"];
6. expect_that!(value, elements_are!(eq(&"foo"), lt(&"xyz"), starts_with("b")));
7. }

If we change the last element to "!", the test fails with a structured error message pin-pointing the error:

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

This slide should take about 5 minutes.

  • GoogleTest is not part of the Rust Playground, so you need to run this example in a local environment. Use cargo add googletest to quickly add it to an existing Cargo project.
  • The use googletest::prelude::*; line imports a number of commonly used macros and types.
  • 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:
1. #[test]
2. fn test_multiline_string_diff() {
3. let haiku = "Memory safety found,\n\
4. Rust's strong typing guides the way,\n\
5. Secure code you'll write.";
6. assert_that!(
7. haiku,
8. eq("Memory safety found,\n\
9. Rust's silly humor guides the way,\n\
10. Secure code you'll write.")
11. );
12. }

shows a color-coded diff (colors not shown here):

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