tests: migrate ops test to bats

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

tests/ops/exec/env/valid/main.cue

@@ -0,0 +1,15 @@
+package testing
+
+#up: [
+	{
+		do:  "fetch-container"
+		ref: "alpine"
+	},
+	{
+		do: "exec"
+		args: ["sh", "-c", """
+			[ "$foo" == "output environment" ] || exit 1
+			"""]
+		env: foo: "output environment"
+	},
+]