Move Mockall and GoogleTest slides to Android section (#1533)

After #1528 and #1532, we now have actual slides which showcase the
crates in action. So we can reclaim a few minutes by removing the slide
which mentions Mockall and GoogleTest slide.

The slide mentioned [proptest](https://docs.rs/proptest) and
[rstest](https://docs.rs/rstest) as well. While I'm sure the libraries
are useful, we don't have them imported into AOSP and I've never
personally used them. We should therefore not advertise them yet at this
point since they won't be useful to Android engineers.

Of course we can mention things that are not in AOSP (or in Chromium),
but I think we should do it in the speaker notes at most.

Cargo.lock

@@ -59,6 +59,14 @@ dependencies = [
  "url",
 ]
 
+[[package]]
+name = "android-testing"
+version = "0.1.0"
+dependencies = [
+ "googletest",
+ "mockall",
+]
+
 [[package]]
 name = "android-tzdata"
 version = "0.1.1"
@@ -2372,10 +2380,6 @@ checksum = "3369f5ac52d5eb6ab48c6b4ffdc8efbcad6b89c765749064ba298f2c68a16a76"
 [[package]]
 name = "testing"
 version = "0.1.0"
-dependencies = [
- "googletest",
- "mockall",
-]
 
 [[package]]
 name = "thiserror"

Cargo.toml

@@ -3,6 +3,7 @@
 members = [
   "mdbook-course",
   "mdbook-exerciser",
+  "src/android/testing",
   "src/bare-metal/useful-crates/allocator-example",
   "src/bare-metal/useful-crates/zerocopy-example",
   "src/borrowing",

book.toml

@@ -197,7 +197,10 @@ use-boolean-and = true
 "structs/tuple-structs.html" = "../user-defined-types/tuple-structs.html"
 "structure.html" = "running-the-course/course-structure.html"
 "testing/doc-tests.html" = "../testing/other.html"
+"testing/googletest.html" = "../android/testing/googletest.html"
 "testing/integration-tests.html" = "../testing/other.html"
+"testing/mockall.html" = "../android/testing/mockall.html"
+"testing/useful-crates.html" = "../testing.html"
 "traits.html" = "methods-and-traits/traits.html"
 "traits/closures.html" = "../std-traits/closures.html"
 "traits/default-methods.html" = "../methods-and-traits/traits.html"

mdbook-course/src/bin/course-schedule.rs

@@ -45,7 +45,7 @@ fn timediff(actual: u64, target: u64, slop: u64) -> String {
             duration(actual),
             duration(actual - target),
         )
-    } else if actual < target - slop {
+    } else if actual + slop < target {
         format!("{}: ({} short)", duration(actual), duration(target - actual),)
     } else {
         format!("{}", duration(actual))

src/SUMMARY.md

@@ -178,9 +178,6 @@
 - [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)
@@ -231,6 +228,9 @@
     - [Sending Objects](android/aidl/types/objects.md)
     - [Parcelables](android/aidl/types/parcelables.md)
     - [Sending Files](android/aidl/types/file-descriptor.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
+
+Building 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/android/testing/Cargo.toml

@@ -0,0 +1,21 @@
+[package]
+name = "android-testing"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[[example]]
+name = "googletest-example"
+crate-type = ["staticlib"]
+path = "googletest.rs"
+test = true
+
+[[example]]
+name = "mockall-example"
+crate-type = ["staticlib"]
+path = "mockall.rs"
+test = true
+
+[dependencies]
+googletest = "0.11.0"
+mockall = "0.12.1"

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/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");
+    }
+}

src/testing/Cargo.toml

@@ -4,22 +4,6 @@ version = "0.1.0"
 edition = "2021"
 publish = false
 
-[[example]]
-name = "googletest-example"
-crate-type = ["staticlib"]
-path = "googletest.rs"
-test = true
-
-[[example]]
-name = "mockall-example"
-crate-type = ["staticlib"]
-path = "mockall.rs"
-test = true
-
 [[bin]]
 name = "luhn"
 path = "exercise.rs"
-
-[dependencies]
-googletest = "0.11.0"
-mockall = "0.12.1"

src/testing/useful-crates.md

@@ -1,15 +0,0 @@
----
-minutes: 3
----
-
-# Useful Crates
-
-Rust comes with only basic support for writing tests.
-
-Here are some additional crates which we recommend for writing tests:
-
-- [googletest](https://docs.rs/googletest): Comprehensive test assertion library
-  in the tradition of GoogleTest for C++.
-- [proptest](https://docs.rs/proptest): Property-based testing for Rust.
-- [rstest](https://docs.rs/rstest): Support for fixtures and parameterised
-  tests.