Add slide on GoogleTest (#1528)

We expect Android engineers to start using this crate going forward.

src/SUMMARY.md

@@ -172,6 +172,7 @@
   - [Test Modules](testing/unit-tests.md)
   - [Other Types of Tests](testing/other.md)
   - [Useful Crates](testing/useful-crates.md)
+  - [GoogleTest](testing/googletest.md)
   - [Compiler lints and Clippy](testing/lints.md)
   - [Exercise: Luhn Algorithm](testing/exercise.md)
     - [Solution](testing/solution.md)

src/testing/Cargo.toml

@@ -4,7 +4,15 @@ version = "0.1.0"
 edition = "2021"
 publish = false
 
+[[example]]
+name = "googletest-example"
+crate-type = ["staticlib"]
+path = "googletest.rs"
+test = true
+
 [[bin]]
 name = "luhn"
 path = "exercise.rs"
 
+[dependencies]
+googletest = "0.10.0"

src/testing/googletest.md

@@ -0,0 +1,73 @@
+---
+minutes: 5
+---
+
+# GoogleTest
+
+The [GoogleTest](https://docs.rs/googletest/) crate allows for flexible test
+assertions using _matchers_:
+
+```rust,ignore
+{{#include googletest.rs:test_elements_are}}
+```
+
+If we change the last element to `"!"`, the test fails with a structured error
+message pin-pointing the error:
+
+<!-- mdbook-xgettext: skip -->
+
+```text
+---- 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
+```
+
+<details>
+
+- 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][prelude].
+
+- This just scratches the surface, there are many builtin matchers.
+
+- A particularly nice feature is that mismatches in multi-line strings strings
+  are shown as a diff:
+
+```rust,ignore
+{{#include googletest.rs:test_multiline_string_diff}}
+```
+
+  shows a color-coded diff (colors not shown here):
+
+  <!-- mdbook-xgettext: skip -->
+  ```text
+      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
+  ```
+
+- The crate is a Rust port of
+  [GoogleTest for C++](https://google.github.io/googletest/).
+
+[prelude]: https://docs.rs/googletest/latest/googletest/prelude/index.html
+
+- GoogleTest is available for use in AOSP.
+
+</details>

src/testing/googletest.rs

@@ -0,0 +1,25 @@
+// ANCHOR: test_elements_are
+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")));
+}
+// ANCHOR_END: test_elements_are
+
+#[should_panic]
+// ANCHOR: test_multiline_string_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.")
+    );
+}
+// ANCHOR_END: test_multiline_string_diff