`update_exact` test failed if `git depth` equals to 1

Problem

update_exact test failed if git depth equals to 1

Steps

Run these commands (Travis buildlog):

% git clone --depth 1 https://github.com/rust-lang/rustup.rs
% cargo test --test cli-self-upd --target x86_64-unknown-linux-gnu --features vendored-openssl -- update_exact
running 2 tests
test rustup_self_update_exact ... ok
test update_exact ... FAILED

failures:

---- update_exact stdout ----
running "/home/lzutao/rust-fork/rustup.rs/target/tests/rustup-exe.9r2QibNMrMCh/rustup" "set" "default-host" "x86_64-unknown-linux-gnu"
status: exit code: 0
----- stdout

----- stderr

running "/home/lzutao/rust-fork/rustup.rs/target/tests/rustup-exe.9r2QibNMrMCh/rustup-init" "-y"
status: exit code: 0
----- stdout

  stable installed - 1.1.0 (hash-s-2)


Rust is installed now. Great!

To get started you need Cargo's bin directory
(/home/lzutao/rust-fork/rustup.rs/target/tests/rustup-cargo.ctxqsympdsec/ch/bin)
in your PATH environment variable. Next time you log in this will be done
automatically.

To configure your current shell run
source /home/lzutao/rust-fork/rustup.rs/target/tests/rustup-cargo.ctxqsympdsec/ch/env

----- stderr
info: syncing channel updates for 'stable-x86_64-unknown-linux-gnu'
info: latest update on 2015-01-02, rust version 1.1.0
info: downloading component 'rust-std'
info: downloading component 'rustc'
info: downloading component 'cargo'
info: downloading component 'rust-docs'
info: installing component 'rust-std'
info: installing component 'rustc'
info: installing component 'cargo'
info: installing component 'rust-docs'
info: default toolchain set to 'stable'

running "/home/lzutao/rust-fork/rustup.rs/target/tests/rustup-exe.9r2QibNMrMCh/rustup" "self" "update"
status: exit code: 0
----- stdout

----- stderr
info: checking for self-updates
info: downloading self-update
info: rustup updated successfully to 2019-04-19


> rustup self update
out.ok: true
out.stdout (0 lines):

out.stderr (3 lines):
    info: checking for self-updates
    info: downloading self-update
    info: rustup updated successfully to 2019-04-19

expected.ok: true
expected.stdout (0 lines):

expected.stderr (3 lines):
    info: checking for self-updates
    info: downloading self-update
    info: rustup updated successfully to 1.17.0

[tests/mock/clitools.rs:228] out.stdout == stdout = true
[tests/mock/clitools.rs:229] out.stderr == stderr = false
thread 'main' panicked at 'explicit panic', tests/mock/clitools.rs:230:9
note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.


failures:
    update_exact

test result: FAILED. 1 passed; 1 failed; 0 ignored; 0 measured; 55 filtered out

error: test failed, to rerun pass '--test cli-self-upd'

Possible Solution(s)

Not at this time. I'm planning to have a look at git-testament crate.

Start with the cli-self-upd test target and its update_exact test, then inspect tests/mock/clitools.rs around the reported output comparison. Read the git-testament crate as suggested and reproduce the failure from a depth-1 clone with the command in the issue. Done means update_exact passes with the shallow checkout and its expected output remains correct.