Add integration tests running bat with empty input files.

tests/integration_tests.rs

@@ -76,6 +76,58 @@ fn concatenate_stdin() {
         .stdout("hello world\nstdin\nhello world\n");
 }
 
+#[test]
+fn concatenate_empty_first() {
+    bat()
+        .arg("empty.txt")
+        .arg("test.txt")
+        .assert()
+        .success()
+        .stdout("hello world\n");
+}
+
+#[test]
+fn concatenate_empty_last() {
+    bat()
+        .arg("test.txt")
+        .arg("empty.txt")
+        .assert()
+        .success()
+        .stdout("hello world\n");
+}
+
+#[test]
+fn concatenate_empty_both() {
+    bat()
+        .arg("empty.txt")
+        .arg("empty.txt")
+        .assert()
+        .success()
+        .stdout("");
+}
+
+#[test]
+fn concatenate_empty_between() {
+    bat()
+        .arg("test.txt")
+        .arg("empty.txt")
+        .arg("test.txt")
+        .assert()
+        .success()
+        .stdout("hello world\nhello world\n");
+}
+
+#[test]
+fn concatenate_empty_first_and_last() {
+    bat()
+        .arg("empty.txt")
+        .arg("test.txt")
+        .arg("empty.txt")
+        .assert()
+        .success()
+        .stdout("hello world\n");
+}
+
 #[test]
 fn line_numbers() {
     bat()