If active insulin is < 0, use 0 for active insulin in simple bolus calculator (#328)

Author: ps2

Loop.xcodeproj/project.pbxproj

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Loop/Models/SimpleBolusCalculator.swift

@@ -28,7 +28,8 @@ struct SimpleBolusCalculator {
                 let correctionTarget = correctionRange.averageValue(for: .milligramsPerDeciliter)
                 let correctionBolus = (manualGlucose.doubleValue(for: .milligramsPerDeciliter) - correctionTarget) / sensitivity
                 if correctionBolus >= 0 {
-                    let correctionBolusMinusActiveInsulin = correctionBolus - activeInsulin.doubleValue(for: .internationalUnit())
+                    let activeInsulin = max(0, activeInsulin.doubleValue(for: .internationalUnit()))
+                    let correctionBolusMinusActiveInsulin = correctionBolus - activeInsulin
                     recommendedBolus += max(0, correctionBolusMinusActiveInsulin)
                 } else {
                     recommendedBolus += correctionBolus

LoopTests/Models/SimpleBolusCalculatorTests.swift

@@ -60,6 +60,19 @@ class SimpleBolusCalculatorTests: XCTestCase {
 
         XCTAssertEqual(0.0, recommendation.doubleValue(for: .internationalUnit()), accuracy: 0.01)
     }
+    
+    func testCorrectionRecommendationWithNegativeIOB() {
+        let recommendation = SimpleBolusCalculator.recommendedInsulin(
+            mealCarbs: nil,
+            manualGlucose: HKQuantity(unit: .milligramsPerDeciliter, doubleValue: 180),
+            activeInsulin: HKQuantity(unit: .internationalUnit(), doubleValue: -1),
+            carbRatioSchedule: carbRatioSchedule,
+            correctionRangeSchedule: correctionRangeSchedule,
+            sensitivitySchedule: sensitivitySchedule)
+        
+        XCTAssertEqual(0.94, recommendation.doubleValue(for: .internationalUnit()), accuracy: 0.01)
+    }
+
 
     func testCorrectionRecommendationWhenInRange() {
         let recommendation = SimpleBolusCalculator.recommendedInsulin(