diff --git a/Cargo.lock b/Cargo.lock
index 5c589fa97ef..2fee7af5122 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -468,6 +468,12 @@ dependencies = [
  "syn 1.0.109",
 ]
 
+[[package]]
+name = "difflib"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6184e33543162437515c2e2b48714794e37845ec9851711914eec9d308f6ebe8"
+
 [[package]]
 name = "digest"
 version = "0.10.7"
@@ -478,6 +484,12 @@ dependencies = [
  "crypto-common",
 ]
 
+[[package]]
+name = "downcast"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1435fa1053d8b2fbbe9be7e97eca7f33d37b28409959813daefc1446a14247f1"
+
 [[package]]
 name = "dtoa"
 version = "1.0.9"
@@ -499,6 +511,12 @@ version = "0.6.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3a68a4904193147e0a8dec3314640e6db742afd5f6e634f428a6af230d9b3591"
 
+[[package]]
+name = "either"
+version = "1.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a26ae43d7bcc3b814de94796a5e736d4029efb0ee900c12e2d54c993ad1a1e07"
+
 [[package]]
 name = "elasticlunr-rs"
 version = "3.0.2"
@@ -575,6 +593,15 @@ dependencies = [
  "windows-sys",
 ]
 
+[[package]]
+name = "float-cmp"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "98de4bbd547a563b716d8dfa9aad1cb19bfab00f4fa09a6a4ed21dbcf44ce9c4"
+dependencies = [
+ "num-traits",
+]
+
 [[package]]
 name = "fnv"
 version = "1.0.7"
@@ -605,6 +632,12 @@ dependencies = [
  "percent-encoding",
 ]
 
+[[package]]
+name = "fragile"
+version = "2.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c2141d6d6c8512188a7891b4b01590a45f6dac67afb4f255c4124dbb86d4eaa"
+
 [[package]]
 name = "fsevent-sys"
 version = "4.1.0"
@@ -1031,6 +1064,15 @@ dependencies = [
 name = "iterators"
 version = "0.1.0"
 
+[[package]]
+name = "itertools"
+version = "0.10.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b0fd2260e829bddf4cb6ea802289de2f86d6a7a690192fbe91b3f46e0f2c8473"
+dependencies = [
+ "either",
+]
+
 [[package]]
 name = "itoa"
 version = "1.0.9"
@@ -1258,6 +1300,33 @@ dependencies = [
  "windows-sys",
 ]
 
+[[package]]
+name = "mockall"
+version = "0.11.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4c84490118f2ee2d74570d114f3d0493cbf02790df303d2707606c3e14e07c96"
+dependencies = [
+ "cfg-if",
+ "downcast",
+ "fragile",
+ "lazy_static",
+ "mockall_derive",
+ "predicates",
+ "predicates-tree",
+]
+
+[[package]]
+name = "mockall_derive"
+version = "0.11.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "22ce75669015c4f47b289fd4d4f56e894e4c96003ffdf3ac51313126f94c6cbb"
+dependencies = [
+ "cfg-if",
+ "proc-macro2",
+ "quote",
+ "syn 1.0.109",
+]
+
 [[package]]
 name = "native-tls"
 version = "0.2.11"
@@ -1282,6 +1351,12 @@ version = "1.0.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e4a24736216ec316047a1fc4252e27dabb04218aa4a3f37c6e7ddbf1f9782b54"
 
+[[package]]
+name = "normalize-line-endings"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "61807f77802ff30975e01f4f071c8ba10c022052f98b3294119f3e615d13e5be"
+
 [[package]]
 name = "normpath"
 version = "1.1.1"
@@ -1617,6 +1692,36 @@ version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "925383efa346730478fb4838dbe9137d2a47675ad789c546d150a6e1dd4ab31c"
 
+[[package]]
+name = "predicates"
+version = "2.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "59230a63c37f3e18569bdb90e4a89cbf5bf8b06fea0b84e65ea10cc4df47addd"
+dependencies = [
+ "difflib",
+ "float-cmp",
+ "itertools",
+ "normalize-line-endings",
+ "predicates-core",
+ "regex",
+]
+
+[[package]]
+name = "predicates-core"
+version = "1.0.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b794032607612e7abeb4db69adb4e33590fa6cf1149e95fd7cb00e634b92f174"
+
+[[package]]
+name = "predicates-tree"
+version = "1.0.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "368ba315fb8c5052ab692e68a0eefec6ec57b23a36959c14496f0b0df2c0cecf"
+dependencies = [
+ "predicates-core",
+ "termtree",
+]
+
 [[package]]
 name = "pretty_env_logger"
 version = "0.5.0"
@@ -2210,11 +2315,18 @@ dependencies = [
  "windows-sys",
 ]
 
+[[package]]
+name = "termtree"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3369f5ac52d5eb6ab48c6b4ffdc8efbcad6b89c765749064ba298f2c68a16a76"
+
 [[package]]
 name = "testing"
 version = "0.1.0"
 dependencies = [
  "googletest",
+ "mockall",
 ]
 
 [[package]]
diff --git a/src/SUMMARY.md b/src/SUMMARY.md
index bb38b993f6a..5e71c8f8373 100644
--- a/src/SUMMARY.md
+++ b/src/SUMMARY.md
@@ -173,6 +173,7 @@
   - [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)
diff --git a/src/testing/Cargo.toml b/src/testing/Cargo.toml
index 657993f00ef..6cb5ffc1cb4 100644
--- a/src/testing/Cargo.toml
+++ b/src/testing/Cargo.toml
@@ -10,9 +10,16 @@ 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 = "0.10.0"
+mockall = "0.11.4"
\ No newline at end of file
diff --git a/src/testing/mockall.rs b/src/testing/mockall.rs
new file mode 100644
index 00000000000..7ca6bc976bb
--- /dev/null
+++ b/src/testing/mockall.rs
@@ -0,0 +1,13 @@
+use std::time::Duration;
+
+#[mockall::automock]
+pub trait Pet {
+    fn is_hungry(&self, since_last_meal: Duration) -> bool;
+}
+
+#[test]
+fn test_robot_pet() {
+    let mut mock_dog = MockPet::new();
+    mock_dog.expect_is_hungry().return_const(true);
+    assert_eq!(mock_dog.is_hungry(Duration::from_secs(10)), true);
+}
diff --git a/src/testing/mocking.md b/src/testing/mocking.md
new file mode 100644
index 00000000000..ca8e49b0e78
--- /dev/null
+++ b/src/testing/mocking.md
@@ -0,0 +1,58 @@
+---
+minutes: 5
+---
+
+# Mocking
+
+If you want to do mocking, we recommend [Mockall]. You need to refactor your
+code to use traits, which you can then quickly mock:
+
+```rust,ignore
+{{#include mockall.rs}}
+```
+
+[Mockall]: https://docs.rs/mockall/
+
+<details>
+
+- Note that *mocking is controversial*: mocks allow you to completely isolate a
+  test from its dependencies. The immediate result is faster and more stable
+  test execution. On the other hand, the mocks can be configured wrongly and
+  return output different from what the real dependencies would do.
+
+  If at all possible, it is recommended that you use the real dependencies. As
+  an example, many databases allow you to configure an in-memory backend. This
+  means that you get the correct behavior in your tests, plus they are fast and
+  will automatically clean up after themselves.
+
+  Similarly, many web frameworks allow you to start an in-process server which
+  binds to a random port on `localhost`. Always prefer this over mocking away
+  the framework since it helps you test your code in the real environment.
+
+- Mockall is not part of the Rust Playground, so you need to run this example in
+  a local environment. Use `cargo add mockall` to quickly add Mockall to an
+  existing Cargo project.
+
+- Mockall has a lot more functionality. In particular, you can set up
+  expectations which depend on the arguments passed:
+
+    ```rust,ignore
+    let mut mock_cat = MockPet::new();
+    mock_cat
+        .expect_is_hungry()
+        .with(mockall::predicate::gt(Duration::from_secs(3 * 3600)))
+        .return_const(true);
+    mock_cat
+        .expect_is_hungry()
+        .return_const(true);
+    assert_eq!(mock_cat.is_hungry(Duration::from_secs(1 * 3600)), false);
+    assert_eq!(mock_cat.is_hungry(Duration::from_secs(5 * 3600)), true);
+    ```
+
+- You can use `.times(n)` to limit the number of times a mock method can be
+  called to `n` --- the mock will automatically panic when dropped if this isn't
+  satisfied.
+
+- Mockall is available for use in AOSP.
+
+</details>