diff --git a/README.md b/README.md
index 212a2d5..df5cfbc 100644
--- a/README.md
+++ b/README.md
@@ -1,7 +1,7 @@
 # itconfig
 [![Build Status](https://travis-ci.org/icetemple/itconfig-rs.svg?branch=master)](https://travis-ci.org/icetemple/itconfig-rs)
 [![Documentation](https://docs.rs/itconfig/badge.svg)](https://docs.rs/itconfig)
-[![Crates.io](https://img.shields.io/badge/crates.io-v0.10.0-orange.svg?longCache=true)](https://crates.io/crates/itconfig) 
+[![Crates.io](https://img.shields.io/badge/crates.io-v0.10.1-orange.svg?longCache=true)](https://crates.io/crates/itconfig) 
 [![Join the chat at https://gitter.im/icetemple/itconfig-rs](https://badges.gitter.im/icetemple/itconfig-rs.svg)](https://gitter.im/icetemple/itconfig-rs?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 
 Easy build a configs from environment variables and use it in globally.
diff --git a/itconfig/Cargo.toml b/itconfig/Cargo.toml
index 3cebc52..49130e6 100644
--- a/itconfig/Cargo.toml
+++ b/itconfig/Cargo.toml
@@ -25,34 +25,10 @@ failure = { version = "0.1.6", features = ["derive"]}
 default = ["macro", "numbers", "bool"]
 macro = []
 
-numbers = [
-    "int",
-    "uint",
-    "float"
-]
-
-int = [
-    "i8",
-    "i16",
-    "i32",
-    "i64",
-    "i128",
-    "isize",
-]
-
-uint = [
-    "u8",
-    "u16",
-    "u32",
-    "u64",
-    "u128",
-    "usize",
-]
-
-float = [
-    "f32",
-    "f64",
-]
+numbers = ["int", "uint", "float"]
+int = ["i8", "i16", "i32", "i64", "i128", "isize"]
+uint = ["u8", "u16", "u32", "u64", "u128", "usize"]
+float = ["f32", "f64"]
 
 i8    = []
 i16   = []
diff --git a/itconfig_tests/tests/get_env.rs b/itconfig_tests/tests/get_env.rs
index f8baaa8..f6b9459 100644
--- a/itconfig_tests/tests/get_env.rs
+++ b/itconfig_tests/tests/get_env.rs
@@ -1,23 +1,74 @@
 use std::env;
 use itconfig::*;
+use itconfig::EnvError::*;
 
 #[test]
 #[should_panic(expected = "Environment variable \"TEST_CASE_1\" is missing")]
-fn missing_env_variable() {
+fn get_missing_env() {
     get_env_or_panic::<String>("TEST_CASE_1");
 }
 
 #[test]
 #[should_panic(expected = "Failed to parse environment variable \"TEST_CASE_2\"")]
-fn cannot_parse_env_variable() {
-    env::set_var("TEST_CASE_2", "30r");
-    get_env_or_panic::<u32>("TEST_CASE_2");
+fn get_env_with_invalid_value() {
+    let env_name = "TEST_CASE_2";
+    env::set_var(&env_name, "30r");
+    get_env_or_panic::<u32>(env_name);
 }
 
 #[test]
-fn get_env_successfully() {
-    env::set_var("TEST_CASE_3", "30");
-    let a = get_env::<u32>("TEST_CASE_3").unwrap();
-
-    assert_eq!(a, 30);
+fn get_result_of_missing_env() {
+    let env_name = String::from("TEST_CASE_3");
+    let env_val = get_env::<String>(&env_name);
+    assert_eq!(env_val, Err(MissingVariable { env_name }))
+}
+
+#[test]
+fn get_result_of_env_with_invalid_value() {
+    let env_name = String::from("TEST_CASE_4");
+    env::set_var(&env_name, "30r");
+    let env_val = get_env::<u32>(&env_name);
+    assert_eq!(env_val, Err(FailedToParse { env_name }))
+}
+
+#[test]
+fn get_result_of_env_successfully() {
+    env::set_var("TEST_CASE_5", "30");
+    let env_var = get_env("TEST_CASE_5");
+    assert_eq!(env_var, Ok(30));
+}
+
+#[test]
+fn get_missing_env_with_default_value() {
+    let flag: bool = get_env_or_default("TEST_CASE_6", "true");
+    assert_eq!(flag, true);
+}
+
+#[test]
+#[should_panic(expected = "Failed to parse environment variable \"TEST_CASE_7\"")]
+fn get_invalid_env_with_default_value() {
+    env::set_var("TEST_CASE_7", "30r");
+    get_env_or_default::<u32, _>("TEST_CASE_7", 30);
+}
+
+#[test]
+#[should_panic(expected = "Failed to parse environment variable \"TEST_CASE_8\"")]
+fn get_env_with_invalid_default_value() {
+    get_env_or_default::<u32, _>("TEST_CASE_8", "30r");
+}
+
+#[test]
+fn get_env_with_default_successfully() {
+    env::set_var("TEST_CASE_9", "10");
+    let env_val: u32 = get_env_or_default("TEST_CASE_9", 30);
+    assert_eq!(env_val, 10)
+}
+
+#[test]
+fn get_missing_env_with_set_default_value() {
+    let flag: bool = get_env_or_set_default("TEST_CASE_10", "true");
+    assert_eq!(flag, true);
+
+    let env_var = env::var("TEST_CASE_10");
+    assert_eq!(env_var, Ok(String::from("true")))
 }
diff --git a/itconfig_tests/tests/get_env_or_default.rs b/itconfig_tests/tests/get_env_or_default.rs
deleted file mode 100644
index 70a86cf..0000000
--- a/itconfig_tests/tests/get_env_or_default.rs
+++ /dev/null
@@ -1,28 +0,0 @@
-use std::env;
-use itconfig::*;
-
-#[test]
-fn missing_env_variable() {
-    let flag: bool = get_env_or_default("DEFAULT_TEST_CASE_1", "true");
-    assert_eq!(flag, true);
-}
-
-#[test]
-#[should_panic(expected = "Failed to parse environment variable \"DEFAULT_TEST_CASE_2\"")]
-fn cannot_parse_env_variable() {
-    env::set_var("DEFAULT_TEST_CASE_2", "30r");
-    let _: u32 = get_env_or_default("DEFAULT_TEST_CASE_2", 30);
-}
-
-#[test]
-#[should_panic(expected = "Failed to parse environment variable \"DEFAULT_TEST_CASE_2\"")]
-fn cannot_parse_default_value() {
-    let _: u32 = get_env_or_default("DEFAULT_TEST_CASE_2", "30r");
-}
-
-#[test]
-fn get_env_successfully() {
-    let a: u32 = get_env_or_default("DEFAULT_TEST_CASE_3", 30);
-
-    assert_eq!(a, 30);
-}