Mask insta env vars in integration tests (#579)

cargo-insta/tests/main.rs

@@ -111,15 +111,25 @@ impl TestProject {
  }
  fn cmd(&self) -> Command {
  let mut command = Command::new(env!("CARGO_BIN_EXE_cargo-insta"));
+ // Remove environment variables so we don't inherit anything (such as
+ // `INSTA_FORCE_PASS` or `CARGO_INSTA_*`) from a cargo-insta process
+ // which runs this integration test.
+ for (key, _) in env::vars() {
+ if key.starts_with("CARGO_INSTA") || key.starts_with("INSTA") {
+ command.env_remove(&key);
+ }
+ }
+ // Turn off CI flag so that cargo insta test behaves as we expect
+ // under normal operation
+ command.env("CI", "0");
+
  command.current_dir(self.workspace_dir.as_path());
  // Use the same target directory as other tests, consistent across test
  // run. This makes the compilation much faster (though do some tests
  // tread on the toes of others? We could have a different cache for each
  // project if so...)
  command.env("CARGO_TARGET_DIR", target_dir());
- // Turn off CI flag so that cargo insta test behaves as we expect
- // under normal operation
- command.env("CI", "0");
+
  command
  }