diff --git a/.github/workflows/lints.yml b/.github/workflows/lints.yml
index eec548fe..9defa932 100644
--- a/.github/workflows/lints.yml
+++ b/.github/workflows/lints.yml
@@ -18,7 +18,7 @@ jobs:
     steps:
     - uses: actions/checkout@v3
     - run: pip3 install flake8 mypy
-    - run: shellcheck **/*.sh
+    - run: shellcheck **/*.sh bin/verify_duplicate_crates bin/adb-run-test
     - run: python3 -m flake8 .
     # Only include typed Python scripts here.
     - run: python3 -m mypy bin/fetch_archive.py --python-version 3.8 --strict
diff --git a/TESTING.md b/TESTING.md
new file mode 100644
index 00000000..bd1c90bd
--- /dev/null
+++ b/TESTING.md
@@ -0,0 +1,63 @@
+For the most part, libsignal is tested using each language's usual testing infrastructure, as described in the main [README.md](./README.md):
+
+```shell
+# Rust
+% cargo test --workspace --all-features
+
+# Java / Android
+% ./gradlew client:test server:test android:connectedAndroidTest
+
+# Node
+% yarn build && yarn tsc && yarn test
+
+# Swift
+% ./build_ffi.sh --generate-ffi && swift test
+```
+
+However, sometimes there are some more interesting test configurations; those are documented here.
+
+
+# Running cross-compiling Rust tests with custom runners
+
+Rust allows running tests with cross-compiled targets, but normally that only works if your system supports executing the cross-compiled binary (like Intel targets on ARM64 macOS or Windows, or 32-bit targets on 64-bit Linux or Windows). However, by overriding the "runner" setting for a particular target, we can run cross-compiled tests as well.
+
+## Running Rust tests on Android Devices (including the emulator)
+
+1. Connect your device, or start an emulator and let it finish booting.
+
+2. Make sure `adb` is in your path, or set `ADB` to the path to `adb` (it's usually in `$ANDROID_SDK_ROOT/platform-tools/adb`).
+
+3. Set the following environment variables, filling in `path/to/ndk` and `YOUR_HOST_HERE`:
+
+    ```shell
+    ANDROID_NDK_HOME=path/to/ndk
+    CARGO_PROFILE_TEST_STRIP=debuginfo   # make the "push" step take less time
+    CARGO_PROFILE_BENCH_STRIP=debuginfo  # same for benchmarks
+    CARGO_TARGET_AARCH64_LINUX_ANDROID_LINKER=path/to/ndk/toolchains/llvm/prebuilt/YOUR_HOST_HERE/bin/    aarch64-linux-android21-clang
+    CARGO_TARGET_AARCH64_LINUX_ANDROID_RUNNER=bin/adb-run-test # in the repo root
+    ```
+
+    (If working with a different target architecture, don't forget to change the environment variables above. You may need to set additional environment variables depending on what you're building; see [`build_jni.sh`][java/build_jni.sh] for the full set that libsignal-jni uses.)
+
+4. Finally, run `cargo test --target aarch64-linux-android -p PACKAGE`.
+
+When running against an actual device, the "push" step in [`adb-run-test`][bin/adb-run-test] can be a bit flaky. Turning on the developer option "Stay awake" in the system settings seems to help.
+
+You may need to push additional resources if the test expects to find them relative to the working directory, which you can `adb push` as well. (If you're writing the test, prefer `include_bytes!` instead to avoid this.)
+
+
+## Running Rust tests in the iOS Simulator
+
+1. Start a simulator and let it finish booting.
+
+2. Set the following environment variable:
+
+    ```shell
+    CARGO_TARGET_AARCH64_APPLE_IOS_SIM_RUNNER='xcrun simctl spawn booted'
+    ```
+
+    (if working on an Intel Mac, don't forget to change the environment variables above to match the Intel simulator target)
+
+3. Finally, run `cargo test --target aarch64-apple-ios-sim -p PACKAGE`.
+
+If the test has resources found relatively, you’ll have to hack them in by loading them into the simulator’s root, which is located at `~/Developer/CoreSimulator/Devices/YOUR_SIMULATOR_UUID/data`. (If you're writing the test, prefer `include_bytes!` instead to avoid this.)
diff --git a/bin/adb-run-test b/bin/adb-run-test
new file mode 100755
index 00000000..4e005997
--- /dev/null
+++ b/bin/adb-run-test
@@ -0,0 +1,20 @@
+#!/bin/sh
+
+#
+# Copyright 2023 Signal Messenger, LLC.
+# SPDX-License-Identifier: AGPL-3.0-only
+#
+
+set -e
+
+ADB=${ADB:-adb}
+
+executable="$1"
+shift
+basename=$(basename "$executable")
+
+# We have to use /data/local/tmp on modern Android systems;
+# other locations don't allow executables or don't allow non-root adb access by default.
+
+"$ADB" push -z any "$executable" "/data/local/tmp/$basename"
+"$ADB" shell "cd /data/local/tmp/ && chmod 744 $basename && ./$basename" "$@"