`nvm_has` matches shell functions and aliases,
but downloads now run via `command`, which skips them
- a `curl` shell function with no curl binary on the PATH would select the curl path and fail with exit 127,
instead of falling back to an available wget executable.
The new `nvm_has_executable` helper resolves names the same way `command` does, so downloader selection and execution agree.
Add `try` and `try_err` helper functions to `test/common.sh` that capture stdout/stderr and exit code from a single invocation, eliminating duplicate command executions in tests.
Convert all existing tests that used the `OUTPUT`/`EXIT_CODE` double-invocation pattern to use the new helpers.
Also fixes a pre-existing bug in the `nvm_die_on_prefix` test where ASCII apostrophes were used instead of U+2019 to match nvm.sh output.
nvm.sh uses `NVM_SCRIPT_SOURCE="$_"` to detect its source location.
Adding `: nvm.sh` before each source line ensures `$_` is set correctly, preventing breakage when the previous command (e.g., `set -ex`) overwrites it.
Jordan Harband
Peter Dave HelloandJordan Harband
Qiangjun RanandJordan Harband