add eprint test

Signed-off-by: Phil Prasek <[email protected]>

Cargo.toml

@@ -17,6 +17,8 @@ thiserror = "1.0"
 
 [dev-dependencies]
 version-sync = "0.9"
+assert_cmd = "1.0.1"
+predicates = "1.0.8"
 
 [[example]]
 name = "alignment"

tests/mod.rs

@@ -1,3 +1,6 @@
+use assert_cmd::Command;
+use predicates::prelude::*;
+
 #[test]
 fn test_readme_deps() {
     version_sync::assert_markdown_deps_updated!("README.md");
@@ -7,3 +10,12 @@ fn test_readme_deps() {
 fn test_html_root_url() {
     version_sync::assert_html_root_url_updated!("src/lib.rs");
 }
+
+#[test]
+fn test_eprint() {
+    let mut cmd = Command::cargo_bin("examples/hello_world").unwrap();
+
+    // running the CLI with no command returns to std err
+    let result = cmd.assert();
+    result.stderr(predicate::str::contains("Hello, World!"));
+}