add err derive test

err-derive-test/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "err-derive-test"
+version = "0.1.0"
+authors = ["Hatter Jiang <jht5945@gmail.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+err-derive = "0.2.2"

err-derive-test/src/main.rs

@@ -0,0 +1,37 @@
+use err_derive::Error;
+
+#[derive(Debug, Error)]
+pub enum TestError {
+    #[error(display = "invalid attribute (expected: {:?}, got: {:?})", expected, found)]
+    InvalidAttribute {
+        expected: String,
+        found: String,
+    },
+    #[error(display = "missing attribute: {:?}", _0)]
+    MissingAttribute(String),
+}
+
+
+fn main() {
+    println!("-----Error 0-----");
+    if let Err(e) = test_err_0() {
+        println!("{:?}", e);
+        println!("{}", e);
+    }
+    println!("-----Error 1-----");
+    if let Err(e) = test_err_1() {
+        println!("{:?}", e);
+        println!("{}", e);
+    }
+}
+
+fn test_err_0() -> Result<(), TestError> {
+    Err(TestError::MissingAttribute("test".into()))
+}
+
+fn test_err_1() -> Result<(), TestError> {
+    Err(TestError::InvalidAttribute {
+        expected: "aaa".into(),
+        found: "bbbb".into(),
+    })
+}