tests: add tests for jj edit

These tests are very similar to the `jj restore -i` tests because `jj
edit -r $REV` is a specialized version of `jj restore -i --from $REV-
--to $REV` on non-merge commits.

tests/test_edit_command.rs

@@ -0,0 +1,81 @@
+// Copyright 2022 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use crate::common::TestEnvironment;
+
+pub mod common;
+
+#[test]
+fn test_edit() {
+    let mut test_env = TestEnvironment::default();
+    test_env.jj_cmd_success(test_env.env_root(), &["init", "repo", "--git"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    std::fs::write(repo_path.join("file1"), "a\n").unwrap();
+    std::fs::write(repo_path.join("file2"), "a\n").unwrap();
+    std::fs::write(repo_path.join("file3"), "a\n").unwrap();
+    test_env.jj_cmd_success(&repo_path, &["new"]);
+    std::fs::remove_file(repo_path.join("file1")).unwrap();
+    std::fs::write(repo_path.join("file2"), "b\n").unwrap();
+
+    let edit_script = test_env.set_up_fake_diff_editor();
+
+    // Nothing happens if we make no changes
+    std::fs::write(&edit_script, "").unwrap();
+    let stdout = test_env.jj_cmd_success(&repo_path, &["edit"]);
+    insta::assert_snapshot!(stdout, @"Nothing changed.
+");
+    let stdout = test_env.jj_cmd_success(&repo_path, &["diff", "-s"]);
+    insta::assert_snapshot!(stdout, @r###"
+    R file1
+    M file2
+    "###);
+
+    // Nothing happens if the diff-editor exits with an error
+    std::fs::write(&edit_script, "rm file2\0fail").unwrap();
+    let stdout = test_env.jj_cmd_failure(&repo_path, &["edit"]);
+    insta::assert_snapshot!(stdout, @"Error: Failed to edit diff: The diff tool exited with a non-zero code
+");
+    let stdout = test_env.jj_cmd_success(&repo_path, &["diff", "-s"]);
+    insta::assert_snapshot!(stdout, @r###"
+    R file1
+    M file2
+    "###);
+
+    // Can edit changes to individual files
+    std::fs::write(&edit_script, "reset file2").unwrap();
+    let stdout = test_env.jj_cmd_success(&repo_path, &["edit"]);
+    insta::assert_snapshot!(stdout, @r###"
+    Created 8c79910b5033 
+    Working copy now at: 8c79910b5033 
+    Added 0 files, modified 1 files, removed 0 files
+    "###);
+    let stdout = test_env.jj_cmd_success(&repo_path, &["diff", "-s"]);
+    insta::assert_snapshot!(stdout, @"R file1
+");
+
+    // Changes to a commit are propagated to descendants
+    test_env.jj_cmd_success(&repo_path, &["undo"]);
+    std::fs::write(&edit_script, "write file3\nmodified\n").unwrap();
+    let stdout = test_env.jj_cmd_success(&repo_path, &["edit", "-r", "@-"]);
+    insta::assert_snapshot!(stdout, @r###"
+    Created 472de2debaff 
+    Rebased 1 descendant commits
+    Working copy now at: 6d19dc1ea106 
+    Added 0 files, modified 1 files, removed 0 files
+    "###);
+    let contents = String::from_utf8(std::fs::read(repo_path.join("file3")).unwrap()).unwrap();
+    insta::assert_snapshot!(contents, @"modified
+");
+}