Unit testing CSV parsing logic - csv

Question

I'm using the CSV crate to read CSV files. I then parse the content. I would like to unit test the parsing logic. Here's a simplified version of the code:
fn main() -> Result<(), Box<dyn Error>> {
let mut rdr = csv::ReaderBuilder::new()
.from_path("test.csv")?;
process(rdr.records());
Ok(())
}
fn process(iter: StringRecordsIter<File>) -> Result<String, String> {
for result in iter {
// Parsing takes place here
println!("{:?}", result);
}
// Post-parsing using entire file content takes place here
Ok(String::from("My Result Here"))
}
In my unit test I would like to be able to construct sequences of StringRecord objects, pass them to the process() method and validate the results. I can successfully create a StringRecord using the simple StringRecord::new() and fill it with values using record.push_field("my field value"). However, I'm struggling to create an iterator that returns my values to pass to the process(). Any suggestions? I'm happy to change the arguments to process() if this makes things easier.

Answer 1

The suggestion made by Jmb to change the signature of process() to fn process(iter: impl Iterator<Item = csv::Result<StringRecord>>) -> Result<String, String> works nicely.
Here's the solution in detail. Firstly the only change to process() is to make it accept more types:
fn process(iter: impl Iterator<Item = csv::Result<StringRecord>>) -> Result<String, String> {
for result in iter {
// Parsing takes place here
println!("{:?}", result);
}
// Post-parsing using entire file content takes place here
Ok(String::from("My Result Here"))
}
The main() remains identical as rdr.records can still be passed to process(). Then the testing looks like this:
#[test]
fn my_test() -> Result<(), String> {
let record1 = result_record(&["Value 1", "Value 2"]);
let record2 = result_record(&["Value 3", "Value 4"]);
let records = vec![record1, record2];
let result = process(records.into_iter())?;
assert_eq!("My Result Here", result);
Ok(())
}
fn result_record(fields: &[&str]) -> csv::Result<StringRecord> {
let mut record = StringRecord::new();
for field in fields {
record.push_field(field);
}
Ok(record)
}