test(format): Verify null where supported

Can't add json5 to this yet becaue its broken

Author: epage

tests/testsuite/file_json.rs

@@ -16,6 +16,7 @@ fn test_file() {
         place: Place,
         #[serde(rename = "arr")]
         elements: Vec<String>,
+        nullable: Option<String>,
     }
 
     #[derive(Debug, Deserialize)]
@@ -52,7 +53,8 @@ fn test_file() {
     }
   },
   "FOO": "FOO should be overridden",
-  "bar": "I am bar"
+  "bar": "I am bar",
+  "nullable": null
 }
 "#,
             FileFormat::Json,
@@ -92,6 +94,7 @@ fn test_file() {
             "John Smith".to_owned()
         );
     }
+    assert_eq!(s.nullable, None);
 }
 
 #[test]

tests/testsuite/file_ron.rs

@@ -16,6 +16,7 @@ fn test_file() {
         place: Place,
         #[serde(rename = "arr")]
         elements: Vec<String>,
+        nullable: Option<String>,
     }
 
     #[derive(Debug, Deserialize)]
@@ -54,7 +55,8 @@ fn test_file() {
     }
   ),
   FOO: "FOO should be overridden",
-  bar: "I am bar"
+  bar: "I am bar",
+  nullable: None
 )
 "#,
             FileFormat::Ron,
@@ -95,6 +97,7 @@ fn test_file() {
             "John Smith".to_owned()
         );
     }
+    assert_eq!(s.nullable, None);
 }
 
 #[test]

tests/testsuite/file_yaml.rs

@@ -18,6 +18,7 @@ fn test_file() {
         place: Place,
         #[serde(rename = "arr")]
         elements: Vec<String>,
+        nullable: Option<String>,
     }
 
     #[derive(Debug, Deserialize)]
@@ -52,6 +53,7 @@ place:
 # For override tests
 FOO: FOO should be overridden
 bar: I am bar
+nullable: null
 "#,
             FileFormat::Yaml,
         ))
@@ -90,6 +92,7 @@ bar: I am bar
             "John Smith".to_owned()
         );
     }
+    assert_eq!(s.nullable, None);
 }
 
 #[test]