add str traits for split, between, unquote; consolidate tests

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/utils/string/split.rs

@@ -0,0 +1,22 @@
+use super::EMPTY;
+
+type Pair<'a> = (&'a str, &'a str);
+
+/// Split a string with default behaviors on non-match.
+pub trait SplitInfallible<'a> {
+	/// Split a string at the first occurrence of delim. If not found, the
+	/// entire string is returned in \[0\], while \[1\] is empty.
+	fn split_once_infallible(&self, delim: &str) -> Pair<'a>;
+
+	/// Split a string from the last occurrence of delim. If not found, the
+	/// entire string is returned in \[0\], while \[1\] is empty.
+	fn rsplit_once_infallible(&self, delim: &str) -> Pair<'a>;
+}
+
+impl<'a> SplitInfallible<'a> for &'a str {
+	#[inline]
+	fn rsplit_once_infallible(&self, delim: &str) -> Pair<'a> { self.rsplit_once(delim).unwrap_or((self, EMPTY)) }
+
+	#[inline]
+	fn split_once_infallible(&self, delim: &str) -> Pair<'a> { self.split_once(delim).unwrap_or((self, EMPTY)) }
+}