add regression test read from file

e2etests/e2e_test.go

@@ -239,3 +239,16 @@ md: |md
 a -> md -> b
 `, md)
 }
+
+func loadFromFile(t *testing.T, name string) testCase {
+	fn := filepath.Join("testdata", "files", fmt.Sprintf("%s.d2", name))
+	d2Text, err := ioutil.ReadFile(fn)
+	if err != nil {
+		t.Fatalf("failed to load test from file:%s. %s", name, err.Error())
+	}
+
+	return testCase{
+		name:   name,
+		script: string(d2Text),
+	}
+}

e2etests/regression_test.go

@@ -573,6 +573,7 @@ b
 }
 `,
 		},
+		loadFromFile(t, "unconnected"),
 	}
 
 	runa(t, tcs)

e2etests/testdata/files/unconnected.d2

@@ -0,0 +1,35 @@
+title: Workflow-I (Warehousing, Installation) {
+  near: top-center
+  shape: text
+  style: {
+    font-size: 40
+    bold: false
+    underline: false
+  }
+}
+OEM Factory
+OEM Factory -> OEM Warehouse
+OEM Factory -> Distributor Warehouse
+OEM Factory -> Gos Warehouse
+direction: right
+Gos Warehouse.Master -> Gos Warehouse.Regional-1
+Gos Warehouse.Master -> Gos Warehouse.Regional-2
+Gos Warehouse.Master -> Gos Warehouse.Regional-N
+Gos Warehouse.Regional-1 -> Gos Warehouse.Regional-2
+Gos Warehouse.Regional-2 -> Gos Warehouse.Regional-N
+Gos Warehouse.Regional-N -> Gos Warehouse.Regional-1
+
+Gos Warehouse.explaination: |`md
+  - Asset Tagging
+  - Inventory
+  - Staging
+  - Dispatch to Site
+`|
+
+OEM Warehouse -> Gos Warehouse
+Distributor Warehouse -> Gos Warehouse
+
+Customer Site: {
+  Installation
+  Support
+}