Revise WASI documentation for swift test commands (#1595)

Updated links and commands for running WebAssembly tests with `swift test`.

---------

Co-authored-by: Jonathan Grynspan <jgrynspan@apple.com>
Co-authored-by: Joseph Heck <j_heck@apple.com>

Author: 3 people

Documentation/WASI.md

@@ -14,31 +14,52 @@ See https://swift.org/CONTRIBUTORS.txt for Swift project authors
 because it provides instructions the reader must follow directly. -->
 
 To run tests for WebAssembly, install a Swift SDK for WebAssembly by following
-[these instructions](https://book.swiftwasm.org/getting-started/setup.html).
+[these instructions](https://www.swift.org/documentation/articles/wasm-getting-started.html).
 
-Because `swift test` doesn't know what WebAssembly environment you'd like to use
-to run your tests, building tests and running them are two separate steps. To
-build tests for WebAssembly, use the following command:
+
+In Swift 6.3 and later, running `swift test --swift-sdk <wasm_swift_sdk_id>`
+builds and runs your tests. Use `jq` to extract the Swift SDK ID automatically
+to build and test in a single command:
+
+swift test --swift-sdk \
+  "$(swiftc -print-target-info | jq -r '.swiftCompilerTag')_wasm"
+```
+
+## Build and Test WebAssembly separately
+
+Prior to Swift 6.3, `swift test` doesn't support `--swift-sdk` option to
+indicate the WebAssembly environment to use for tests. In this case, building
+tests and running them are two separate steps. To build tests for WebAssembly,
+use the following command:
 
 ```sh
-swift build --swift-sdk wasm32-unknown-wasi --build-tests
+swift build \
+  --swift-sdk "$(swiftc -print-target-info | jq -r '.swiftCompilerTag')_wasm" \
+  --build-tests
 ```
 
-After building tests, you can run them using a [WASI](https://wasi.dev/)-compliant
-WebAssembly runtime such as [Wasmtime](https://wasmtime.dev/) or
-[WasmKit](https://github.com/swiftwasm/WasmKit). For example, to run tests using
-Wasmtime, use the following command (replace `{YOURPACKAGE}` with your package's
-name):
+After building tests, you can run them using
+a [WASI](https://wasi.dev/)-compliant WebAssembly runtime such as
+[WasmKit](https://github.com/swiftwasm/WasmKit). WasmKit is included in
+the Swift toolchain for Linux and macOS for Swift 6.2 and later.
+[Download and install an open-source release toolchain from swift.org](https://swift.org/install)
+to get a toolchain that includes WasmKit.
+
+To run the rests you built previously using the WasmKit runtime, use the
+following command, replacing `{YOURPACKAGE}` with the name of your package:
 
 ```sh
-wasmtime .build/debug/{YOURPACKAGE}PackageTests.wasm --testing-library swift-testing
+wasmkit run .build/debug/{YOURPACKAGE}PackageTests.wasm \
+  --testing-library swift-testing
 ```
 
-Most WebAssembly runtimes forward trailing arguments to the WebAssembly program,
-so you can pass command-line options of the testing library. For example, to list
-all tests and filter them by name, use the following commands:
+Most WebAssembly runtimes forward trailing arguments to the WebAssembly
+program, so you can pass command-line options of the testing library. For
+example, to list all tests and filter them by name, use the following commands:
 
 ```sh
-wasmtime .build/debug/{YOURPACKAGE}PackageTests.wasm list --testing-library swift-testing
-wasmtime .build/debug/{YOURPACKAGE}PackageTests.wasm --testing-library swift-testing --filter "FoodTruckTests.foodTruckExists"
+wasmkit run .build/debug/{YOURPACKAGE}PackageTests.wasm list \
+  --testing-library swift-testing
+wasmkit run .build/debug/{YOURPACKAGE}PackageTests.wasm \
+  --testing-library swift-testing --filter "FoodTruckTests.foodTruckExists"
 ```