fix: import into a cluster that has no such database yet

src/cmd/postgres.rs

@@ -21,8 +21,10 @@ pub struct DropDb<'a> {
 
 impl Cmd for DropDb<'_> {
     fn argv(&self) -> Argv {
+        // a cluster that never held this database is still a restore target
         Argv::new("dropdb")
             .flag("--username", self.username)
+            .arg("--if-exists")
             .arg(self.dbname)
     }
 }
@@ -174,9 +176,22 @@ impl Cmd for PgDumpAll<'_> {
 
 #[cfg(test)]
 mod tests {
-    use super::{PgDump, Psql};
+    use super::{DropDb, PgDump, Psql};
     use crate::cmd::Cmd;
 
+    #[test]
+    fn a_missing_database_is_not_a_failed_import() {
+        assert_eq!(
+            DropDb {
+                username: "u",
+                dbname: "db",
+            }
+            .argv()
+            .quoted(),
+            "dropdb --username u --if-exists db"
+        );
+    }
+
     #[test]
     fn a_directory_dump_names_the_file_it_writes() {
         assert_eq!(