message: Don't use real serde in tests
diff: @@ -2298,26 +2298,40 @@ fn pass_correct_cfgs_flags_to_rustdoc() {
  authors = []
  [features]
  - default = ["serde_codegen"]
  - nightly = ["serde_derive"]
  + default = ["mock_serde_codegen"]
  + nightly = ["mock_serde_derive"]
  [dependencies]
  - serde_derive = { version = "0.8", optional = true }
  + mock_serde_derive = { path = "../mock_serde_derive", optional = true }
  [build-dependencies]
  - serde_codegen = { version = "0.8", optional = true }
  + mock_serde_codegen = { path = "../mock_serde_codegen", optional = true }
  "#)
  .file("libs/feature_a/src/lib.rs", r#"
  - #[cfg(feature = "serde_derive")]
  + #[cfg(feature = "mock_serde_derive")]
  const MSG: &'static str = "This is safe";
  - #[cfg(feature = "serde_codegen")]
  + #[cfg(feature = "mock_serde_codegen")]
  const MSG: &'static str = "This is risky";
  pub fn get() -> &'static str {
  MSG
  }
  - "#);
  + "#)
  + .file("libs/mock_serde_derive/Cargo.toml", r#"
  + [package]
  + name = "mock_serde_derive"
  + version = "0.1.0"
  + authors = []
  + "#)
  + .file("libs/mock_serde_derive/src/lib.rs", "")
  + .file("libs/mock_serde_codegen/Cargo.toml", r#"
  + [package]
  + name = "mock_serde_codegen"
  + version = "0.1.0"
  + authors = []
  + "#)
  + .file("libs/mock_serde_codegen/src/lib.rs", "");
  assert_that(p.cargo_process("test")
  .arg("--package").arg("feature_a")
  @@ -2325,7 +2339,7 @@ fn pass_correct_cfgs_flags_to_rustdoc() {
  execs().with_status(0)
  .with_stderr_contains("\
  [DOCTEST] feature_a
  -[RUNNING] `rustdoc --test [..]serde_codegen[..]`"));
  +[RUNNING] `rustdoc --test [..]mock_serde_codegen[..]`"));
  assert_that(p.cargo_process("test")
  .arg("--verbose"),
  