Adding tests

Signed-off-by: dubo-dubon-duponey <dubodubonduponey+github@pm.me>

examples/tests/exec/invalid/main.cue

@@ -0,0 +1,13 @@
+package testing
+
+#dagger: compute: [
+	{
+		do: "fetch-container"
+		ref: "alpine"
+	},
+	{
+		do: "exec"
+		// XXX Blocked by https://github.com/blocklayerhq/dagger/issues/19
+		dir: "/"
+	},
+}