Add an integration test for reading data from stdin

tests/integration.rs

@@ -3,10 +3,9 @@
 // For the full copyright and license information, please view the LICENSE-*
 // files that was distributed with this source code.
 
-use assert_cmd::prelude::*;
+use assert_cmd::cmd::Command;
 use predicates::prelude::*;
 use std::io::Write;
-use std::process::Command;
 use tempfile::NamedTempFile;
 
 // Integration tests for the diffutils command
@@ -161,3 +160,46 @@ fn missing_newline() -> Result<(), Box<dyn std::error::Error>> {
         .stderr(predicate::str::starts_with("No newline at end of file"));
     Ok(())
 }
+
+#[test]
+fn read_from_stdin() -> Result<(), Box<dyn std::error::Error>> {
+    let mut file1 = NamedTempFile::new()?;
+    file1.write_all("foo\n".as_bytes())?;
+    let mut file2 = NamedTempFile::new()?;
+    file2.write_all("bar\n".as_bytes())?;
+
+    let mut cmd = Command::cargo_bin("diffutils")?;
+    cmd.arg("-u")
+        .arg(file1.path())
+        .arg("-")
+        .write_stdin("bar\n");
+    cmd.assert()
+        .code(predicate::eq(1))
+        .failure()
+        .stdout(predicate::eq(format!(
+            "--- {}\t\n+++ /dev/stdin\t\n@@ -1 +1 @@\n-foo\n+bar\n",
+            file1.path().to_string_lossy()
+        )));
+
+    let mut cmd = Command::cargo_bin("diffutils")?;
+    cmd.arg("-u")
+        .arg("-")
+        .arg(file2.path())
+        .write_stdin("foo\n");
+    cmd.assert()
+        .code(predicate::eq(1))
+        .failure()
+        .stdout(predicate::eq(format!(
+            "--- /dev/stdin\t\n+++ {}\t\n@@ -1 +1 @@\n-foo\n+bar\n",
+            file2.path().to_string_lossy()
+        )));
+
+    let mut cmd = Command::cargo_bin("diffutils")?;
+    cmd.arg("-u").arg("-").arg("-").write_stdin("foo\n");
+    cmd.assert()
+        .code(predicate::eq(0))
+        .success()
+        .stdout(predicate::str::is_empty());
+
+    Ok(())
+}