Add basic tests for tsIntersectionOf

Author: mitchell-merry

test/utils.test.ts

@@ -1,4 +1,5 @@
 import { tsUnionOf } from "../src/utils";
+import { tsIntersectionOf } from "../src/utils";
 
 describe("utils", () => {
   describe("tsUnionOf", () => {
@@ -18,4 +19,26 @@ describe("utils", () => {
       return expect(tsUnionOf(...[0, true, "string", '"hello"'])).toBe('0 | true | string | "hello"');
     });
   });
+
+  describe("tsIntersectionOf", () => {
+    const tests: [string, string[], string][] = [
+      ["identity for single type", ["string"], "string"],
+      ["basic intersection", ["string", "number"], "string & number"],
+      ["filter out unknown", ["string", "number", "unknown"], "string & number"],
+      ["identity for unknown type", ["unknown"], "unknown"],
+      ["unknown for no types passed", [], "unknown"],
+      ["parentheses around types with union", ["4", `string | number`], "4 & (string | number)"],
+      [
+        "parentheses around types with intersection",
+        ["{ red: string }", "{ blue: string } & { green: string }"],
+        "{ red: string } & ({ blue: string } & { green: string })",
+      ],
+    ];
+
+    tests.forEach(([name, input, output]) => {
+      test(name, () => {
+        expect(tsIntersectionOf(...input)).toBe(output);
+      });
+    });
+  });
 });