refactor: Move parser configuration and add tests

bin/src/main.rs

@@ -1,4 +1,6 @@
-use std::{error::Error, ffi::OsStr, fs};
+mod parser_configuration;
+
+use std::{error::Error, fs};
 
 use clap::Parser;
 
@@ -22,28 +24,15 @@ struct Args {
     merge_path: std::path::PathBuf,
 }
 
-fn get_parser_configuration_by_file_path(
-    file_path: &std::path::PathBuf,
-) -> Result<parsing::ParserConfiguration, String> {
-    file_path
-        .extension()
-        .and_then(OsStr::to_str)
-        .and_then(|extension| match extension {
-            "java" => Some(model::Language::Java),
-            _ => None,
-        })
-        .map(parsing::ParserConfiguration::from)
-        .ok_or(format!("Could not retrieve parsing configuration for file {}", file_path.display()))
-}
-
 fn main() -> Result<(), Box<dyn Error>> {
     let args = Args::parse();
-    
+
     let base = fs::read_to_string(&args.base_path)?;
     let left = fs::read_to_string(args.left_path)?;
     let right = fs::read_to_string(args.right_path)?;
-
-    let parser_configuration = get_parser_configuration_by_file_path(&args.base_path)?;
+
+    let parser_configuration =
+        parser_configuration::get_parser_configuration_by_file_path(&args.base_path)?;
 
     let base_tree = parsing::parse_string(&base, &parser_configuration).unwrap();
     let left_tree = parsing::parse_string(&left, &parser_configuration).unwrap();

bin/src/parser_configuration.rs

@@ -0,0 +1,33 @@
+pub fn get_parser_configuration_by_file_path(
+    file_path: &std::path::Path,
+) -> Result<parsing::ParserConfiguration, String> {
+    file_path
+        .extension()
+        .and_then(std::ffi::OsStr::to_str)
+        .and_then(|extension| match extension {
+            "java" => Some(model::Language::Java),
+            _ => None,
+        })
+        .map(parsing::ParserConfiguration::from)
+        .ok_or(format!(
+            "Could not retrieve parsing configuration for file {}",
+            file_path.display()
+        ))
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::parser_configuration::get_parser_configuration_by_file_path;
+
+    #[test]
+    fn if_the_file_extension_has_no_parser_available_it_returns_error() {
+        let file_path = std::path::PathBuf::from("/path/without/extension");
+        assert!(get_parser_configuration_by_file_path(&file_path).is_err())
+    }
+
+    #[test]
+    fn if_the_file_extension_has_a_parser_available_it_returns_error() {
+        let file_path = std::path::PathBuf::from("/path/for/java/file/Example.java");
+        assert!(get_parser_configuration_by_file_path(&file_path).is_ok())
+    }
+}