Add test for docker example

Signed-off-by: Tom Chauveau <tom.chauveau@epitech.eu>

tests/stdlib/docker/build/Dockerfile

@@ -0,0 +1,2 @@
+FROM alpine
+RUN echo test >> /test.txt

tests/stdlib/docker/build/build.cue

@@ -0,0 +1,31 @@
+package docker
+
+import (
+	"dagger.io/dagger"
+	"dagger.io/dagger/op"
+	"dagger.io/docker"
+)
+
+// Build a Docker image from source, using included Dockerfile
+source: dagger.#Artifact
+
+TestBuild: {
+	image: docker.#Build & {
+		"source": source
+	}
+
+	verify: #up: [
+		op.#Load & {
+			from: image
+		},
+
+		op.#Exec & {
+			always: true
+			args: [
+				"sh", "-c", """
+						grep -q "test" /test.txt
+					""",
+			]
+		},
+	]
+}