[fine] Type testing with probes and reporting

I'm proud of the test harness here actually. Also fix a bug in
checking!

fine/tests/example_tests.rs

@@ -1,4 +1,5 @@
 use fine::parser::SyntaxTree;
+use fine::semantics::{Semantics, Type};
 use fine::tokens::Lines;
 use pretty_assertions::assert_eq;
 
@@ -70,7 +71,7 @@ fn rebase_concrete(source_path: &str, dump: &str) {
 }
 
 fn assert_concrete(tree: &SyntaxTree, expected: &str, source_path: &str) {
-    let dump = tree.dump();
+    let dump = tree.dump(false);
     let rebase = std::env::var("FINE_TEST_REBASE")
         .unwrap_or(String::new())
         .to_lowercase();
@@ -85,12 +86,52 @@ fn assert_concrete(tree: &SyntaxTree, expected: &str, source_path: &str) {
 }
 
 fn assert_type_at(
-    _tree: &SyntaxTree,
-    _lines: &Lines,
-    _pos: usize,
-    _expected: &str,
+    tree: &SyntaxTree,
+    lines: &Lines,
+    pos: usize,
+    expected: &str,
     _source_path: &str,
 ) {
+    let tree_ref = match tree.find_tree_at(pos) {
+        Some(t) => t,
+        None => {
+            println!("Unable to find the subtee at position {pos}! Parsed the tree as:");
+            println!("\n{}", tree.dump(true));
+            panic!("Cannot find tree at position {pos}");
+        }
+    };
+
+    let semantics = Semantics::new(tree, lines);
+    let tree_type = semantics.type_of(tree_ref, true);
+
+    let actual = format!("{}", tree_type.unwrap_or(Type::Error));
+    if actual != expected {
+        println!(
+            "The type of the {:?} tree at position {pos} had the wrong type! Parsed the tree as:",
+            tree[tree_ref].kind
+        );
+        println!("\n{}", tree.dump(true));
+
+        let errors = semantics.snapshot_errors();
+        if errors.len() == 0 {
+            println!("There were no errors reported during type checking.\n");
+        } else {
+            println!(
+                "{} error{} reported during type checking:",
+                errors.len(),
+                if errors.len() == 1 { "" } else { "s" }
+            );
+            for error in &errors {
+                println!("  Error: {error}");
+            }
+            println!();
+        }
+
+        assert_eq!(
+            expected, actual,
+            "The type of the tree at position {pos} was incorrect"
+        );
+    }
 }
 
 include!(concat!(env!("OUT_DIR"), "/generated_tests.rs"));