add test for history::add

src/history/add.rs

@@ -15,3 +15,75 @@ pub fn add(link: &Link, file_name: &str) -> Result<()> {
     writeln!(file, "{}", link.href)?;
     Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+
+    use crate::{
+        history::Link,
+        test_utils::{create_text_file, read_text_file},
+    };
+
+    use super::*;
+
+    #[test]
+    fn creates_file_if_missing() -> Result<()> {
+        //given
+        let (dir, file_name) =
+            create_text_file("download.txt", include_bytes!("../../test/data/empty.txt"))?;
+        std::fs::remove_file(&file_name)?;
+
+        let link = Link {
+            href: "foo".to_string(),
+            rel: "bar".to_string(),
+            hreflang: None,
+            mime_type: None,
+            title: None,
+            length: None,
+        };
+        //when
+        add(&link, &file_name)?;
+
+        //then
+        let content: Vec<String> = read_text_file(&file_name)?;
+        drop(dir);
+
+        let expected = vec!["foo".to_string()];
+        assert_eq!(content, expected);
+
+        Ok(())
+    }
+
+    #[test]
+    fn appends_to_exising_file() -> Result<()> {
+        // given
+        let (dir, file_name) = create_text_file(
+            "download.txt",
+            include_bytes!("../../test/data/downloads.txt"),
+        )?;
+
+        let link = Link {
+            href: "foo".to_string(),
+            rel: "bar".to_string(),
+            hreflang: None,
+            mime_type: None,
+            title: None,
+            length: None,
+        };
+        //when
+        add(&link, &file_name)?;
+
+        //then
+        let content: Vec<String> = read_text_file(&file_name)?;
+        drop(dir);
+
+        let expected = vec![
+            "line-1".to_string(),
+            "line-2".to_string(),
+            "foo".to_string(),
+        ];
+        assert_eq!(content, expected);
+
+        Ok(())
+    }
+}

src/test_utils.rs

@@ -1,4 +1,8 @@
-use std::{fs::File, io::Write, str::from_utf8};
+use std::{
+    fs::{read_to_string, File},
+    io::Write,
+    str::from_utf8,
+};
 
 use tempfile::{tempdir, TempDir};
 
@@ -12,3 +16,10 @@ pub fn create_text_file(name: &str, data: &[u8]) -> Result<(TempDir, String)> {
     write!(&file, "{data}")?;
     Ok((dir, filename))
 }
+
+pub fn read_text_file(file_name: &str) -> Result<Vec<String>> {
+    Ok(read_to_string(file_name)?
+        .lines()
+        .map(String::from)
+        .collect())
+}

test/data/downloads.txt

@@ -0,0 +1,2 @@
+line-1
+line-2