Reinstate type checks in Math.min and Math.max

tests/lib/math/min_max_test.dart

Index: tests/lib/math/min_max_test.dart
diff --git a/tests/lib/math/min_max_test.dart b/tests/lib/math/min_max_test.dart
index 46d05665e7af66f3d93457b953aab0099d9cbd92..a2ce160b9421f29fc8fe6debe2cc33b8e1732097 100644
--- a/tests/lib/math/min_max_test.dart
+++ b/tests/lib/math/min_max_test.dart
@@ -11,10 +11,27 @@ import 'dart:math';
 var inf = double.INFINITY;
 var nan = double.NAN;
 
+// A class that might work if [min] and [max] worked for non-numbers.
+class Wrap implements Comparable {
+  final value;
+  Wrap(this.value);
+  int compare(Wrap other) => value.compare(other.value);
+  bool operator<(Wrap other) => compare(other) < 0;
+  bool operator<=(Wrap other) => compare(other) <= 0;
+  bool operator>(Wrap other) => compare(other) > 0;
+  bool operator>=(Wrap other) => compare(other) >= 0;
+  bool operator==(other) => other is Wrap && compare(other) == 0;
+  String toString() => 'Wrap($value)';
+}
+
+var wrap1 = new Wrap(1);
+var wrap2 = new Wrap(2);
+
 testMin() {
   testMin1();
   testMin2();
   testMin3();
+  testMinChecks();
 }
 
 testMin1() {
@@ -279,10 +296,18 @@ testMin3() {
   Expect.isFalse(min(inf, inf).isNegative);
 }
 
+testMinChecks() {
+  // Min and max work only on numbers.
+  Expect.throws(() => min(wrap1, wrap2), (e) => e is ArgumentError);
+  Expect.throws(() => min(wrap1, 0), (e) => e is ArgumentError);
+  Expect.throws(() => min(0, wrap2), (e) => e is ArgumentError);
+}
+
 testMax() {
   testMax1();
   testMax2();
   testMax3();
+  testMaxChecks();
 }
 
 testMax1() {
@@ -537,6 +562,13 @@ testMax3() {
   Expect.isTrue(max(-inf, -inf).isNegative);
 }
 
+testMaxChecks() {
+  // Min and max work only on numbers.
+  Expect.throws(() => min(wrap1, wrap2), (e) => e is ArgumentError);
+  Expect.throws(() => min(wrap1, 0), (e) => e is ArgumentError);
+  Expect.throws(() => min(0, wrap2), (e) => e is ArgumentError);
+}
+
 main() {
   testMin();
   testMin();