Add InEpsilon().

assert/assertions.go

@@ -537,6 +537,39 @@ func InDelta(t TestingT, expected, actual interface{}, delta float64, msgAndArgs
 	return true
 }
 
+// InEpsilon asserts that expected and actual have a relative error less than epsilon
+//
+// Returns whether the assertion was successful (true) or not (false).
+func InEpsilon(t TestingT, expected, actual interface{}, epsilon 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...)
+	}
+
+	if af < 0 {
+		af = -af
+	}
+	if bf < 0 {
+		bf = -bf
+	}
+	var delta float64
+	if af < bf {
+		delta = af * epsilon
+	} else {
+		delta = bf * epsilon
+	}
+
+	// delta = min(|expected|, |actual|) * epsilon
+	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
+}
+
 /*
 	Errors
 */