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Chris Biscardi

Using assert_fs, predicates, and assert_cmd to integration test bins that spawn subcommands and write files

Our cargo binary is named garden and it calls out to get user input multiple times, including calling EDITOR and asking for user responses on stdout.

First we'll create a fake editor script to use instead of vim, etc.

tests/fake_editor.sh is a one-liner.

shell
echo "testing" >> $1;

Then we'll write our test using assert_cmd to build up a Command that points to the garden binary in out Cargo.toml.

We grab the fake editor path script using std::env::current_dir(), make sure the file exists (which means we've grabbed the right path), and spawn a new Command with the EDITOR variable set to the fake editor script. The equivalent call to our bin is:

rust
EDITOR=path/to/fake-editor.sh garden write -t atitle

And the rust code to execute.

rust
#[test]
fn test_write_with_title() {
let mut cmd = Command::cargo_bin("garden").unwrap();
let fake_editor_path = std::env::current_dir()
.expect("expect to be in a dir")
.join("tests")
.join("fake-editor.sh");
if !fake_editor_path.exists() {
panic!(
"fake editor shell script could not be found"
)
}
let assert = cmd
.env("EDITOR", fake_editor_path.into_os_string())
.arg("write")
.arg("-t")
.arg("atitle")
.write_stdin("N\n".as_bytes())
.assert();
assert.success();
}

Note that we're asserting that the command exited sucessfully, and that we're inputing N\n to the bin's stdin, which responds to a request for user input after the editor closes.

Note that this doesn't actually test for the resulting file existence, and also that we're writing our files out directly into our default digital garden! We can solve this with assert_fs and predicates.

We'll bring in both preludes and create a new temporary directory.

a prelude is a bunch of stuff the library author thinks will be useful to have around all the time

We'll use the GARDEN_PATH environment variable to pass the temporary directory in to the garden bin and that's it, we've added a temporary directory to our test.

No more polluting the default garden!

rust
use assert_fs::prelude::*;
use predicates::prelude::*;
#[test]
fn test_write_with_title() {
let temp_dir = assert_fs::TempDir::new().unwrap();
let mut cmd = Command::cargo_bin("garden").unwrap();
let fake_editor_path = std::env::current_dir()
.expect("expect to be in a dir")
.join("tests")
.join("fake-editor.sh");
if !fake_editor_path.exists() {
panic!(
"fake editor shell script could not be found"
)
}
let assert = cmd
.env("EDITOR", fake_editor_path.into_os_string())
.env("GARDEN_PATH", temp_dir.path())
.arg("write")
.arg("-t")
.arg("atitle")
.write_stdin("N\n".as_bytes())
.assert();
assert.success();
}

Now that's enough, but we can also check to make sure the file we expect to exist actually exists. temp_dir.child gives us the possible file, and we can assert on that file with a test from predicates that tests to make sure the file exists.

rust
temp_dir
.child("atitle.md")
.assert(predicate::path::exists());