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exercises/02_basic_calculator/05_factorial/src/lib.rs

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+// Define a function named `factorial` that, given a non-negative integer `n`,
+// returns `n!`, the factorial of `n`.
+//
+// The factorial of `n` is defined as the product of all positive integers up to `n`.
+// For example, `5!` (read "five factorial") is `5 * 4 * 3 * 2 * 1`, which is `120`.
+// `0!` is defined to be `1`.
+//
+// We expect `factorial(0)` to return `1`, `factorial(1)` to return `1`,
+// `factorial(2)` to return `2`, and so on.
+//
+// Use only what you learned! No loops yet, so you'll have to use recursion!
+
+#[cfg(test)]
+mod tests {
+    use crate::factorial;
+
+    #[test]
+    fn first() {
+        assert_eq!(factorial(0), 1);
+    }
+
+    #[test]
+    fn second() {
+        assert_eq!(factorial(1), 1);
+    }
+
+    #[test]
+    fn third() {
+        assert_eq!(factorial(2), 2);
+    }
+
+    #[test]
+    fn fifth() {
+        assert_eq!(factorial(5), 120);
+    }
+}