tests: add test for jj op log and --at-op

We can't easily test much of the output of `jj op log` because it's
unstable, but here are at least a few tests.

tests/test_operations.rs

@@ -0,0 +1,80 @@
+// 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 std::path::Path;
+
+use crate::common::TestEnvironment;
+
+pub mod common;
+
+#[test]
+fn test_op_log() {
+    let 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");
+
+    let stdout = test_env.jj_cmd_success(&repo_path, &["op", "log"]);
+    insta::assert_snapshot!(redact_op_log(&stdout), @r###"
+    @ 
+    | add workspace 'default'
+    o 
+    initialize repo
+    "###);
+    let add_workspace_id = stdout[2..14].to_string();
+    let initialize_repo_id = stdout.lines().nth(2).unwrap()[2..14].to_string();
+
+    // Can load the repo at a specific operation ID
+    insta::assert_snapshot!(get_log_output(&test_env, &repo_path, &initialize_repo_id), @"o 0000000000000000000000000000000000000000
+");
+    insta::assert_snapshot!(get_log_output(&test_env, &repo_path, &add_workspace_id), @r###"
+    @ 230dd059e1b059aefc0da06a2e5a7dbf22362f22
+    o 0000000000000000000000000000000000000000
+    "###);
+    // "@" resolves to the head operation
+    insta::assert_snapshot!(get_log_output(&test_env, &repo_path, "@"), @r###"
+    @ 230dd059e1b059aefc0da06a2e5a7dbf22362f22
+    o 0000000000000000000000000000000000000000
+    "###);
+
+    // We get a reasonable message if an invalid operation ID is specified
+    insta::assert_snapshot!(test_env.jj_cmd_failure(&repo_path, &["log", "--at-op", "foo"]), @r###"Error: No operation ID matching "foo"
+"###);
+    // Odd length
+    insta::assert_snapshot!(test_env.jj_cmd_failure(&repo_path, &["log", "--at-op", "123456789"]), @r###"Error: No operation ID matching "123456789"
+"###);
+    // Even length
+    insta::assert_snapshot!(test_env.jj_cmd_failure(&repo_path, &["log", "--at-op", "0123456789"]), @r###"Error: No operation ID matching "0123456789"
+"###);
+    // Empty ID
+    // TODO: This is not a reasonable message
+    insta::assert_snapshot!(test_env.jj_cmd_failure(&repo_path, &["log", "--at-op", ""]), @r###"Internal error: Failed to read operation: Other("IO error: Is a directory (os error 21)")
+"###);
+}
+
+fn get_log_output(test_env: &TestEnvironment, repo_path: &Path, op_id: &str) -> String {
+    test_env.jj_cmd_success(repo_path, &["log", "-T", "commit_id", "--at-op", op_id])
+}
+
+fn redact_op_log(stdout: &str) -> String {
+    let mut lines = vec![];
+    for line in stdout.lines() {
+        if line.starts_with("@ ") || line.starts_with("o ") {
+            // Redact everything -- operation ID, user, host, timestamps
+            lines.push(line[..2].to_string());
+        } else {
+            lines.push(line.to_string());
+        }
+    }
+    lines.join("\n")
+}