Fail on error when a statement has no expectations

Sources/DocTest/Statement.swift

@@ -16,17 +16,42 @@ public class Statement {
     }
 
     public func tests(with result: Result<String, REPL.Error>) -> [Test] {
-        let metadata: [String: Any] = [
+        var metadata: [String: Any] = [
             "file": self.sourceLocation.file as Any?,
             "line": self.sourceLocation.line as Any?,
             "column": self.sourceLocation.column as Any?
         ].compactMapValues { $0 }
 
-        return expectations.map { expectation in
-            switch expectation {
-            case .value(let expected):
+        switch result {
+        case .failure(let error):
+            metadata["actual"] = error.description
+
+            if expectations.isEmpty {
+                return [test { .failure("- `\(self.code)` produced an error", directive: nil, metadata: metadata) }]
+            } else {
+                return expectations.map { expectation in
+                    switch expectation {
+                    case .value(let expected):
+                        metadata["expected"] = expected
+
+                        return test {
+                            .failure("- `\(self.code)` produced an error", directive: nil, metadata: metadata)
+                        }
+                    case .error:
+                        return test {
+                            .success("- `\(self.code)` produced an error, as expected", directive: nil, metadata: metadata)
+                        }
+                    }
+                }
+            }
+        case .success(let actual):
+            metadata["actual"] = actual
+
+            return expectations.map { expectation in
+                switch expectation {
+                case .value(let expected):
+                    metadata["expected"] = expected
 
-                if case .success(let actual) = result {
                     if actual == expected {
                         return test {
                             .success("- `\(self.code)` produces `\(actual)`", directive: nil, metadata: metadata)
@@ -36,18 +61,7 @@ public class Statement {
                             .failure("- `\(self.code)` produces `\(actual)`, expected `\(expected)`", directive: nil, metadata: metadata)
                         }
                     }
-
-                } else {
-                    return test {
-                        .failure("- `\(self.code)` did not produce `\(expected)`", directive: nil, metadata: metadata)
-                    }
-                }
-            case .error:
-                if case .failure = result {
-                    return test {
-                        .success("- `\(self.code)` produced an error, as expected", directive: nil, metadata: metadata)
-                    }
-                } else {
+                case .error:
                     return test {
                         .failure("- `\(self.code)` didn't produce an error, which was unexpected", directive: nil, metadata: metadata)
                     }