assert: Fix EqualValues to handle overflow/underflow

The underlying function ObjectsAreEqualValues did not handle
overflow/underflow of values while converting one type to another
for comparison. For example:

    EqualValues(t, int(270), int8(14))

would return true, even though the values are not equal. Because, when
you convert int(270) to int8, it overflows and becomes 14 (270 % 256 = 14)

This commit fixes that by making sure that the conversion always happens
from the smaller type to the larger type, and then comparing the values.
Additionally, this commit also seperates out the test cases of
ObjectsAreEqualValues from TestObjectsAreEqual.

Fixes stretchr#1462

assert/assertions.go

@@ -165,17 +165,40 @@ func ObjectsAreEqualValues(expected, actual interface{}) bool {
 		return true
 	}
 
-	actualType := reflect.TypeOf(actual)
-	if actualType == nil {
+	expectedValue := reflect.ValueOf(expected)
+	actualValue := reflect.ValueOf(actual)
+	if !expectedValue.IsValid() || !actualValue.IsValid() {
 		return false
 	}
-	expectedValue := reflect.ValueOf(expected)
-	if expectedValue.IsValid() && expectedValue.Type().ConvertibleTo(actualType) {
+
+	expectedType := expectedValue.Type()
+	actualType := actualValue.Type()
+	if !expectedType.ConvertibleTo(actualType) {
+		return false
+	}
+
+	if !isNumericType(expectedType) || !isNumericType(actualType) {
 		// Attempt comparison after type conversion
-		return reflect.DeepEqual(expectedValue.Convert(actualType).Interface(), actual)
+		return reflect.DeepEqual(
+			expectedValue.Convert(actualType).Interface(), actual,
+		)
 	}
 
-	return false
+	// If BOTH values are numeric, there are chances of false positives due
+	// to overflow or underflow. So, we need to make sure to always convert
+	// the smaller type to a larger type before comparing.
+	if expectedType.Size() >= actualType.Size() {
+		return actualValue.Convert(expectedType).Interface() == expected
+	}
+
+	return expectedValue.Convert(actualType).Interface() == actual
+}
+
+// isNumericType returns true if the type is one of:
+// int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64,
+// float32, float64
+func isNumericType(t reflect.Type) bool {
+	return t.Kind() >= reflect.Int && t.Kind() <= reflect.Float64
 }
 
 /* CallerInfo is necessary because the assert functions use the testing object

assert/assertions_test.go

@@ -135,24 +135,34 @@ func TestObjectsAreEqual(t *testing.T) {
 
 		})
 	}
+}
 
-	// Cases where type differ but values are equal
-	if !ObjectsAreEqualValues(uint32(10), int32(10)) {
-		t.Error("ObjectsAreEqualValues should return true")
-	}
-	if ObjectsAreEqualValues(0, nil) {
-		t.Fail()
-	}
-	if ObjectsAreEqualValues(nil, 0) {
-		t.Fail()
-	}
+func TestObjectsAreEqualValues(t *testing.T) {
+	now := time.Now()
 
-	tm := time.Now()
-	tz := tm.In(time.Local)
-	if !ObjectsAreEqualValues(tm, tz) {
-		t.Error("ObjectsAreEqualValues should return true for time.Time objects with different time zones")
+	cases := []struct {
+		expected interface{}
+		actual   interface{}
+		result   bool
+	}{
+		{uint32(10), int32(10), true},
+		{0, nil, false},
+		{nil, 0, false},
+		{now, now.In(time.Local), true}, // should be time zone independent
+		{int(270), int8(14), false},     // should handle overflow/underflow
+		{int8(14), int(270), false},
+		{[]int{270, 270}, []int8{14, 14}, false},
 	}
 
+	for _, c := range cases {
+		t.Run(fmt.Sprintf("ObjectsAreEqualValues(%#v, %#v)", c.expected, c.actual), func(t *testing.T) {
+			res := ObjectsAreEqualValues(c.expected, c.actual)
+
+			if res != c.result {
+				t.Errorf("ObjectsAreEqualValues(%#v, %#v) should return %#v", c.expected, c.actual, c.result)
+			}
+		})
+	}
 }
 
 type Nested struct {