Move Mockall and GoogleTest slides to Android

The recommendation to use these crates is really an AOSP
recommendation. People can still use them for general-purpose Rust,
but there are many other useful crates in the wider Rust ecosystem.

src/SUMMARY.md

@@ -172,9 +172,6 @@
 - [Testing](testing.md)
   - [Test Modules](testing/unit-tests.md)
   - [Other Types of Tests](testing/other.md)
-  - [Useful Crates](testing/useful-crates.md)
-  - [GoogleTest](testing/googletest.md)
-  - [Mocking](testing/mocking.md)
   - [Compiler Lints and Clippy](testing/lints.md)
   - [Exercise: Luhn Algorithm](testing/exercise.md)
     - [Solution](testing/solution.md)
@@ -216,6 +213,9 @@
   - [Deploy](android/aidl/deploy.md)
   - [Client](android/aidl/client.md)
   - [Changing API](android/aidl/changing.md)
+- [Testing](android/testing.md)
+  - [GoogleTest](android/testing/googletest.md)
+  - [Mocking](android/testing/mocking.md)
 - [Logging](android/logging.md)
 - [Interoperability](android/interoperability.md)
   - [With C](android/interoperability/with-c.md)

src/android/build_all.sh

@@ -117,6 +117,11 @@ EOF
 
 pkill -f birthday_server
 
+run_example <<EOF
+# ANCHOR: libleftpad_test
+atest --host libleftpad_test
+# ANCHOR_END: libleftpad_test
+EOF
 
 run_example <<EOF
 # ANCHOR: hello_rust_logs

src/android/testing.md

@@ -0,0 +1,37 @@
+# Testing in Android
+
+Buildings on [Testing](../testing.md), we will now look at how unit tests work
+in AOSP. Use the `rust_test` module for your unit tests:
+
+_testing/Android.bp_:
+
+```javascript
+{{#include testing/Android.bp}}
+```
+
+_testing/src/lib.rs_:
+
+```rust
+{{#include testing/src/lib.rs:leftpad}}
+```
+
+You can now run the test with
+
+```shell
+{{#include build_all.sh:libleftpad_test}}
+```
+
+The output looks like this:
+
+```text
+INFO: Elapsed time: 2.666s, Critical Path: 2.40s
+INFO: 3 processes: 2 internal, 1 linux-sandbox.
+INFO: Build completed successfully, 3 total actions
+//comprehensive-rust-android/testing:libleftpad_test_host            PASSED in 2.3s
+    PASSED  libleftpad_test.tests::long_string (0.0s)
+    PASSED  libleftpad_test.tests::short_string (0.0s)
+Test cases: finished with 2 passing and 0 failing out of 2 test cases
+```
+
+Notice how you only mention the root of the library crate. Tests are found
+recursively in nested modules.

src/android/testing/Android.bp

@@ -0,0 +1,13 @@
+rust_library {
+    name: "libleftpad",
+    crate_name: "leftpad",
+    srcs: ["src/lib.rs"],
+}
+
+rust_test {
+    name: "libleftpad_test",
+    crate_name: "leftpad_test",
+    srcs: ["src/lib.rs"],
+    host_supported: true,
+    test_suites: ["general-tests"],
+}

src/testing/googletest.md → src/android/testing/googletest.md

@@ -69,6 +69,4 @@ Difference(-actual / +expected):
 
 [prelude]: https://docs.rs/googletest/latest/googletest/prelude/index.html
 
-- GoogleTest is available for use in AOSP.
-
 </details>

src/testing/mocking.md → src/android/testing/mocking.md

@@ -15,8 +15,7 @@ to use traits, which you can then quickly mock:
 
 <details>
 
-- The advice here is for Android (AOSP) where Mockall is the recommended mocking
-  library. There are other
+- Mockall is the recommended mocking library in Android (AOSP). There are other
   [mocking libraries available on crates.io](https://crates.io/keywords/mock),
   in particular in the area of mocking HTTP services. The other mocking
   libraries work in a similar fashion as Mockall, meaning that they make it easy

src/android/testing/src/lib.rs

@@ -0,0 +1,36 @@
+// Copyright 2024 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// ANCHOR: leftpad
+//! Left-padding library.
+
+/// Left-pad `s` to `width`.
+pub fn leftpad(s: &str, width: usize) -> String {
+    format!("{s:>width$}")
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn short_string() {
+        assert_eq!(leftpad("foo", 5), "  foo");
+    }
+
+    #[test]
+    fn long_string() {
+        assert_eq!(leftpad("foobar", 6), "foobar");
+    }
+}