Add test for log::Level deserialization

Cargo.toml

@@ -53,3 +53,4 @@ glob = "0.3"
 lazy_static = "1"
 notify = "^5.0.0"
 temp-env = "0.3.0"
+log = { version = "0.4", features = ["serde"] }

tests/log.rs

@@ -0,0 +1,56 @@
+extern crate config;
+extern crate log;
+
+#[macro_use]
+extern crate serde_derive;
+extern crate serde_json;
+
+use config::*;
+
+#[derive(Debug, Deserialize)]
+struct Settings {
+    log: log::Level,
+}
+
+fn config(s: &str) -> Config {
+    Config::builder()
+        .add_source(File::from_str(s, FileFormat::Json))
+        .build()
+        .unwrap()
+}
+
+#[test]
+fn test_load_level_uppercase() {
+    let s = r#"{ "log": "ERROR" }"#;
+    let c = config(s);
+    let l = c.get::<log::Level>("log").unwrap();
+    assert_eq!(l, log::Level::Error);
+}
+
+#[test]
+fn test_case_sensitivity_log_level_from_str() {
+    // to verify that this works
+
+    use std::str::FromStr;
+    let l = log::Level::from_str("error").unwrap();
+    assert_eq!(l, log::Level::Error);
+}
+
+#[test]
+fn test_case_sensitivity_json_from_str() {
+    // to confirm serde_json works as expected
+    let s = r#"{ "log": "error" }"#;
+
+    let j: Settings = serde_json::from_str(s).unwrap();
+    assert_eq!(j.log, log::Level::Error);
+}
+
+#[test]
+fn test_load_level_lowercase_succeeding() {
+    let s = r#"{ "log": "error" }"#;
+    let c = config(s);
+    assert_eq!(c.get_string("log").unwrap(), "error");
+    let s = c.try_deserialize::<Settings>();
+    assert!(s.is_ok(), "Expected Ok(_) for {:?}", s);
+    assert_eq!(s.unwrap().log, log::Level::Error);
+}