Add InDelta() for comparing floats.

assert/assertions.go

@@ -475,7 +475,63 @@ func WithinDuration(t TestingT, expected, actual time.Time, delta time.Duration,
 
 	dt := expected.Sub(actual)
 	if dt < -delta || dt > delta {
-		return Fail(t, fmt.Sprintf("Max difference between %v and %v allowed is %v, but difference was %v", expected, actual, dt, delta), msgAndArgs...)
+		return Fail(t, fmt.Sprintf("Max difference between %v and %v allowed is %v, but difference was %v", expected, actual, delta, dt), msgAndArgs...)
+	}
+
+	return true
+}
+
+func toFloat(x interface{}) (float64, bool) {
+	var xf float64
+	xok := true
+
+	switch xn := x.(type) {
+	case uint8:
+		xf = float64(xn)
+	case uint16:
+		xf = float64(xn)
+	case uint32:
+		xf = float64(xn)
+	case uint64:
+		xf = float64(xn)
+	case int:
+		xf = float64(xn)
+	case int8:
+		xf = float64(xn)
+	case int16:
+		xf = float64(xn)
+	case int32:
+		xf = float64(xn)
+	case int64:
+		xf = float64(xn)
+	case float32:
+		xf = float64(xn)
+	case float64:
+		xf = float64(xn)
+	default:
+		xok = false
+	}
+
+	return xf, xok
+}
+
+// InDelta asserts that the two numerals are within delta of each other.
+//
+// 	 assert.InDelta(t, math.Pi, (22 / 7.0), 0.01)
+//
+// Returns whether the assertion was successful (true) or not (false).
+func InDelta(t TestingT, expected, actual interface{}, delta float64, msgAndArgs ...interface{}) bool {
+
+	af, aok := toFloat(expected)
+	bf, bok := toFloat(actual)
+
+	if !aok || !bok {
+		return Fail(t, fmt.Sprintf("Parameters must be numerical"), msgAndArgs...)
+	}
+
+	dt := af - bf
+	if dt < -delta || dt > delta {
+		return Fail(t, fmt.Sprintf("Max difference between %v and %v allowed is %v, but difference was %v", expected, actual, delta, dt), msgAndArgs...)
 	}
 
 	return true

assert/assertions_test.go

@@ -418,3 +418,37 @@ func TestWithinDuration(t *testing.T) {
 	False(t, WithinDuration(mockT, a, b, -11*time.Second), "A 10s difference is not within a 9s time difference")
 	False(t, WithinDuration(mockT, b, a, -11*time.Second), "A 10s difference is not within a 9s time difference")
 }
+
+func TestInDelta(t *testing.T) {
+	mockT := new(testing.T)
+
+	True(t, InDelta(mockT, 1.001, 1, 0.01), "|1.001 - 1| <= 0.01")
+	True(t, InDelta(mockT, 1, 1.001, 0.01), "|1 - 1.001| <= 0.01")
+	True(t, InDelta(mockT, 1, 2, 1), "|1 - 2| <= 1")
+	False(t, InDelta(mockT, 1, 2, 0.5), "Expected |1 - 2| <= 0.5 to fail")
+	False(t, InDelta(mockT, 2, 1, 0.5), "Expected |2 - 1| <= 0.5 to fail")
+	False(t, InDelta(mockT, "", nil, 1), "Expected non numerals to fail")
+
+	cases := []struct {
+		a, b  interface{}
+		delta float64
+	}{
+		{uint8(2), uint8(1), 1},
+		{uint16(2), uint16(1), 1},
+		{uint32(2), uint32(1), 1},
+		{uint64(2), uint64(1), 1},
+
+		{int(2), int(1), 1},
+		{int8(2), int8(1), 1},
+		{int16(2), int16(1), 1},
+		{int32(2), int32(1), 1},
+		{int64(2), int64(1), 1},
+
+		{float32(2), float32(1), 1},
+		{float64(2), float64(1), 1},
+	}
+
+	for _, tc := range cases {
+		True(t, InDelta(mockT, tc.a, tc.b, tc.delta), "Expected |%V - %V| <= %v", tc.a, tc.b, tc.delta)
+	}
+}