add increment and decrement public API to Meter (#132)

motivation: expose increment and decrement public APIs

changes:
* add increment and decrement public API to Meter
* improve the implementation of AccumulatingMeter and TestMeter
* add tests for new APIs
* refactor/modernize other tests

Author: tomerd

Sources/CoreMetrics/Metrics.swift

@@ -231,6 +231,36 @@ public final class Meter {
     public func set<DataType: BinaryFloatingPoint>(_ value: DataType) {
         self._handler.set(Double(value))
     }
+
+    /// Increment the Meter.
+    ///
+    /// - parameters:
+    ///     - by: Amount to increment by.
+    @inlinable
+    public func increment<DataType: BinaryFloatingPoint>(by amount: DataType) {
+        self._handler.increment(by: Double(amount))
+    }
+
+    /// Increment the Meter by one.
+    @inlinable
+    public func increment() {
+        self.increment(by: 1.0)
+    }
+
+    /// Decrement the Meter.
+    ///
+    /// - parameters:
+    ///     - by: Amount to decrement by.
+    @inlinable
+    public func decrement<DataType: BinaryFloatingPoint>(by amount: DataType) {
+        self._handler.decrement(by: Double(amount))
+    }
+
+    /// Decrement the Meter by one.
+    @inlinable
+    public func decrement() {
+        self.decrement(by: 1.0)
+    }
 }
 
 extension Meter {
@@ -787,6 +817,24 @@ internal final class AccumulatingMeter: MeterHandler {
     }
 
     func increment(by amount: Double) {
+        // Drop illegal values
+        // - cannot increment by NaN
+        guard !amount.isNaN else {
+            return
+        }
+        // - cannot increment by infinite quantities
+        guard !amount.isInfinite else {
+            return
+        }
+        // - cannot increment by negative values
+        guard amount.sign == .plus else {
+            return
+        }
+        // - cannot increment by zero
+        guard !amount.isZero else {
+            return
+        }
+
         let newValue: Double = self.lock.withLock {
             self.value += amount
             return self.value
@@ -795,6 +843,24 @@ internal final class AccumulatingMeter: MeterHandler {
     }
 
     func decrement(by amount: Double) {
+        // Drop illegal values
+        // - cannot decrement by NaN
+        guard !amount.isNaN else {
+            return
+        }
+        // - cannot decrement by infinite quantities
+        guard !amount.isInfinite else {
+            return
+        }
+        // - cannot decrement by negative values
+        guard amount.sign == .plus else {
+            return
+        }
+        // - cannot decrement by zero
+        guard !amount.isZero else {
+            return
+        }
+
         let newValue: Double = self.lock.withLock {
             self.value -= amount
             return self.value

Sources/MetricsTestKit/TestMetrics.swift

@@ -57,7 +57,7 @@ public final class TestMetrics: MetricsFactory {
         // nothing to do
     }
 
-    /// Reset method to destroy all created ``TestCounter``, ``TestRecorder`` and ``TestTimer``.
+    /// Reset method to destroy all created ``TestCounter``, ``TestMeter``, ``TestRecorder`` and ``TestTimer``.
     /// Invoke this method in between test runs to verify that Counters are created as needed.
     public func reset() {
         self.lock.withLock {
@@ -361,7 +361,7 @@ public final class TestMeter: TestMetric, MeterHandler, Equatable {
     private var _values = [(Date, Double)]()
 
     init(label: String, dimensions: [(String, String)]) {
-        self.id = NSUUID().uuidString
+        self.id = UUID().uuidString
         self.label = label
         self.dimensions = dimensions
     }
@@ -378,18 +378,54 @@ public final class TestMeter: TestMetric, MeterHandler, Equatable {
     }
 
     public func increment(by amount: Double) {
+        // Drop illegal values
+        // - cannot increment by NaN
+        guard !amount.isNaN else {
+            return
+        }
+        // - cannot increment by infinite quantities
+        guard !amount.isInfinite else {
+            return
+        }
+        // - cannot increment by negative values
+        guard amount.sign == .plus else {
+            return
+        }
+        // - cannot increment by zero
+        guard !amount.isZero else {
+            return
+        }
+
         self.lock.withLock {
-            let lastValue = self._values.last?.1 ?? 0
-            let newValue = lastValue - amount
-            _values.append((Date(), Double(newValue)))
+            let lastValue: Double = self._values.last?.1 ?? 0
+            let newValue = lastValue + amount
+            _values.append((Date(), newValue))
         }
     }
 
     public func decrement(by amount: Double) {
+        // Drop illegal values
+        // - cannot decrement by NaN
+        guard !amount.isNaN else {
+            return
+        }
+        // - cannot decrement by infinite quantities
+        guard !amount.isInfinite else {
+            return
+        }
+        // - cannot decrement by negative values
+        guard amount.sign == .plus else {
+            return
+        }
+        // - cannot decrement by zero
+        guard !amount.isZero else {
+            return
+        }
+
         self.lock.withLock {
-            let lastValue = self._values.last?.1 ?? 0
+            let lastValue: Double = self._values.last?.1 ?? 0
             let newValue = lastValue - amount
-            _values.append((Date(), Double(newValue)))
+            _values.append((Date(), newValue))
         }
     }
 
@@ -428,7 +464,7 @@ public final class TestRecorder: TestMetric, RecorderHandler, Equatable {
     private var _values = [(Date, Double)]()
 
     init(label: String, dimensions: [(String, String)], aggregate: Bool) {
-        self.id = NSUUID().uuidString
+        self.id = UUID().uuidString
         self.label = label
         self.dimensions = dimensions
         self.aggregate = aggregate

Tests/MetricsTests/CoreMetricsTests+XCTest.swift

@@ -46,6 +46,14 @@ extension MetricsTests {
             ("testGaugeBlock", testGaugeBlock),
             ("testMeter", testMeter),
             ("testMeterBlock", testMeterBlock),
+            ("testMeterInt", testMeterInt),
+            ("testMeterFloat", testMeterFloat),
+            ("testMeterIncrement", testMeterIncrement),
+            ("testMeterDecrement", testMeterDecrement),
+            ("testDefaultMeterIgnoresNan", testDefaultMeterIgnoresNan),
+            ("testDefaultMeterIgnoresInfinity", testDefaultMeterIgnoresInfinity),
+            ("testDefaultMeterIgnoresNegativeValues", testDefaultMeterIgnoresNegativeValues),
+            ("testDefaultMeterIgnoresZero", testDefaultMeterIgnoresZero),
             ("testMUX_Counter", testMUX_Counter),
             ("testMUX_Meter", testMUX_Meter),
             ("testMUX_Recorder", testMUX_Recorder),