Test the interaction of inferred and default type parameters

tests/traits.rs

@@ -0,0 +1,45 @@
+use textwrap::{NoHyphenation, Options};
+
+/// Cleaned up type name.
+fn type_name<T: ?Sized>(_val: &T) -> String {
+    std::any::type_name::<T>()
+        .replace("alloc::boxed::Box", "Box")
+        .replace("textwrap::splitting", "textwrap")
+}
+
+#[test]
+fn static_hyphensplitter() {
+    // Inferring the full type.
+    let options = Options::new(10);
+    assert_eq!(
+        type_name(&options),
+        "textwrap::Options<textwrap::HyphenSplitter>"
+    );
+
+    // Explicitly making both parameters inferred.
+    let options: Options<'_, _> = Options::new(10);
+    assert_eq!(
+        type_name(&options),
+        "textwrap::Options<textwrap::HyphenSplitter>"
+    );
+}
+
+#[test]
+fn box_static_nohyphenation() {
+    // Inferred static type.
+    let options = Options::new(10).splitter(Box::new(NoHyphenation));
+    assert_eq!(
+        type_name(&options),
+        "textwrap::Options<Box<textwrap::NoHyphenation>>"
+    );
+}
+
+#[test]
+fn box_dyn_wordsplitter() {
+    // Inferred dynamic type due to default type parameter.
+    let options: Options = Options::new(10).splitter(Box::new(NoHyphenation));
+    assert_eq!(
+        type_name(&options),
+        "textwrap::Options<Box<dyn textwrap::WordSplitter>>"
+    );
+}