support unit testing wasm via wasmtime

build.zig

@@ -73,6 +73,9 @@ pub fn build(b: *std.build.Builder) !void {
         "Build and install test executables with 'build'",
     ) orelse false;
 
+    // We can use wasmtime to test wasm
+    b.enable_wasmtime = true;
+
     // Add our benchmarks
     try benchSteps(b, target, mode);
 
@@ -124,6 +127,15 @@ pub fn build(b: *std.build.Builder) !void {
 
         const step = b.step("wasm", "Build the wasm library");
         step.dependOn(&wasm.step);
+
+        // We support tests via wasmtime. wasmtime uses WASI so this
+        // isn't an exact match to our freestanding target above but
+        // it lets us test some basic functionality.
+        const test_step = b.step("test-wasm", "Run all tests for wasm");
+        const main_test = b.addTest("src/main_wasm.zig");
+        main_test.setTarget(.{ .cpu_arch = .wasm32, .os_tag = .wasi });
+        main_test.addOptions("build_options", exe_options);
+        test_step.dependOn(&main_test.step);
     }
 
     // Run