Add another GPST Gregorian to/from test

Closes #287

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "hifitime"
-version = "4.0.0-alpha.1"
+version = "4.0.0-beta"
 authors = ["Christopher Rabotin <christopher.rabotin@gmail.com>"]
 description = "Ultra-precise date and time handling in Rust for scientific applications with leap second support"
 homepage = "https://nyxspace.com/"

src/epoch/system_time.rs

@@ -15,7 +15,8 @@ use crate::{Duration, Epoch, HifitimeError};
 /// Clippy thinks these are the same type, but they aren't.
 #[allow(clippy::unnecessary_fallible_conversions)]
 pub(crate) fn duration_since_unix_epoch() -> Result<Duration, HifitimeError> {
-    // TODO: Check why there is a map_err and and_then
+    // map_err maps the duration_since error into a hifitime error, if the conversion to a SystemTime fails.
+    // Then we converts a valid SystemTime into a Hifitime duration, unless it fails via and_then
     web_time::SystemTime::now()
         .duration_since(web_time::SystemTime::UNIX_EPOCH)
         .map_err(|_| HifitimeError::SystemTimeError)

tests/epoch.rs

@@ -2069,11 +2069,17 @@ fn regression_test_gh_282() {
 fn regression_test_gh_288() {
     use core::str::FromStr;
     let epoch = Epoch::from_str("2021-03-06 11:14:40.9960 GPST").unwrap();
+    let epoch_from_gpst =
+        Epoch::from_gregorian(2021, 3, 6, 11, 14, 40, 996_000_000, TimeScale::GPST);
 
     assert_eq!(
         "2021-03-06T11:14:40.996000000 GPST",
         format!("{}", epoch.to_gregorian_str(TimeScale::GPST))
     );
+    assert_eq!(
+        format!("{}", epoch_from_gpst.to_gregorian_str(TimeScale::GPST)),
+        format!("{}", epoch.to_gregorian_str(TimeScale::GPST))
+    );
     assert_eq!("2021-03-06T11:14:40.996000000 GPST", format!("{epoch}"));
     assert_eq!(
         "2021-03-06T11:14:40.996000",