universe: spin out js/yarn tests

Signed-off-by: Solomon Hykes <solomon@dagger.io>

stdlib/.dagger/env/js-yarn/plan/yarn.cue

@@ -0,0 +1,26 @@
+package react
+
+import (
+	"dagger.io/dagger"
+	"dagger.io/js/yarn"
+	"dagger.io/alpine"
+	"dagger.io/os"
+)
+
+TestData: dagger.#Artifact
+
+TestReact: {
+	pkg: yarn.#Package & {
+		source: TestData
+	}
+
+	test: os.#Container & {
+		image: alpine.#Image & {
+			package: bash: "=5.1.0-r0"
+		}
+		mount: "/build": from: pkg.build
+		command: """
+			test "$(cat /build/test)" = "output"
+			"""
+	}
+}