Fix conversion to Gregorian

src/duration/kani_verif.rs

@@ -10,7 +10,7 @@
 
 // Here lives all of the formal verification for Duration.
 
-use super::{Duration, DurationError};
+use super::{Duration, DurationError, EpochError};
 use crate::NANOSECONDS_PER_CENTURY;
 
 use kani::Arbitrary;
@@ -43,9 +43,9 @@ fn formal_duration_truncated_ns_reciprocity() {
         // Then it does not fit on a i64, so this function should return an error
         assert_eq!(
             dur_from_part.try_truncated_nanoseconds(),
-            Err(Err(EpochError::Duration {
+            Err(EpochError::Duration {
                 source: DurationError::Overflow,
-            }))
+            })
         );
     } else if centuries == -1 {
         // If we are negative by just enough that the centuries is negative, then the truncated seconds

src/duration/mod.rs

@@ -8,10 +8,8 @@
 * Documentation: https://nyxspace.com/
 */
 
-use crate::errors::DurationError;
-use crate::{
-    EpochError, SECONDS_PER_CENTURY, SECONDS_PER_DAY, SECONDS_PER_HOUR, SECONDS_PER_MINUTE,
-};
+use crate::errors::{DurationError, EpochError};
+use crate::{SECONDS_PER_CENTURY, SECONDS_PER_DAY, SECONDS_PER_HOUR, SECONDS_PER_MINUTE};
 
 pub use crate::{Freq, Frequencies, TimeUnits, Unit};
 
@@ -692,7 +690,15 @@ impl fmt::Display for Duration {
             }
 
             let values = [days, hours, minutes, seconds, milli, us, nano];
-            let units = ["days", "h", "min", "s", "ms", "μs", "ns"];
+            let units = [
+                if days > 1 { "days" } else { "day" },
+                "h",
+                "min",
+                "s",
+                "ms",
+                "μs",
+                "ns",
+            ];
 
             let mut insert_space = false;
             for (val, unit) in values.iter().zip(units.iter()) {
@@ -767,7 +773,7 @@ mod ut_duration {
     fn test_serdes() {
         for (dt, content) in [
             (Duration::from_seconds(10.1), r#""10 s 100 ms""#),
-            (1.0_f64.days() + 99.nanoseconds(), r#""1 days 99 ns""#),
+            (1.0_f64.days() + 99.nanoseconds(), r#""1 day 99 ns""#),
             (
                 1.0_f64.centuries() + 99.seconds(),
                 r#""36525 days 1 min 39 s""#,