fix corner cases in test/reduce (#3709)

test/mocha/reduce.js

@@ -0,0 +1,60 @@
+var assert = require("assert");
+var exec = require("child_process").exec;
+var reduce_test = require("../reduce");
+
+describe("test/reduce.js", function() {
+    it("Should handle test cases with --toplevel", function() {
+        var result = reduce_test([
+            "var Infinity = 42;",
+            "console.log(Infinity);",
+        ].join("\n"), {
+            toplevel: true,
+        });
+        if (result.error) throw result.error;
+        assert.strictEqual(result.code, [
+            "// Can't reproduce test failure with minify options provided:",
+            '// {"toplevel":true}',
+            "",
+        ].join("\n"));
+    });
+    it("Should handle test result of NaN", function() {
+        var result = reduce_test("throw 0 / 0;");
+        if (result.error) throw result.error;
+        assert.strictEqual(result.code, [
+            "// Can't reproduce test failure with minify options provided:",
+            '// {"compress":{},"mangle":false}',
+            "",
+        ].join("\n"));
+    });
+    it("Should print correct output for irreducible test case", function() {
+        var result = reduce_test([
+            "console.log(function f(a) {",
+            "    return f.length;",
+            "}());",
+        ].join("\n"), {
+            compress: {
+                keep_fargs: false,
+            },
+            mangle: false,
+        });
+        if (result.error) throw result.error;
+        assert.strictEqual(result.code, [
+            "console.log(function f(a) {",
+            "    return f.length;",
+            "}());",
+            "// output: 1",
+            "// minify: 0",
+            '// options: {"compress":{"keep_fargs":false},"mangle":false}',
+        ].join("\n"));
+    });
+    it("Should fail when invalid option is supplied", function() {
+        var result = reduce_test("", {
+            compress: {
+                unsafe_regex: true,
+            },
+        });
+        var err = result.error;
+        assert.ok(err instanceof Error);
+        assert.strictEqual(err.stack.split(/\n/)[0], "DefaultsError: `unsafe_regex` is not a supported option");
+    });
+});