[TestJSONEncoder] - Originally we thought the level of precision requested internally by JSONSerialization (via snprintf) could always be two or more digits larger. Turns out it can be any level of precision larger than requested.

Author: bendjones

Darwin/Foundation-swiftoverlay-Tests/TestJSONEncoder.swift

@@ -256,7 +256,7 @@ class TestJSONEncoder : TestJSONEncoderSuper {
             /// our precision requests in every case. This bug effects Darwin, FreeBSD, and Linux currently
             /// causing this test (which uses the current time) to fail occasionally.
             let evalEdgeCase: (Date, Date) -> () = { decodedDate, expectedDate in
-                if formattedLength(of: decodedDate.timeIntervalSinceReferenceDate) > DBL_DECIMAL_DIG + 2 {
+                if formattedLength(of: decodedDate.timeIntervalSinceReferenceDate) > DBL_DECIMAL_DIG {
                     let adjustedTimeIntervalSinceReferenceDate: (Date) -> Double = {
                         let adjustment = pow(10, Double(DBL_DECIMAL_DIG))
                         return Double(floor(adjustment * $0.timeIntervalSinceReferenceDate) / adjustment)
@@ -286,9 +286,15 @@ class TestJSONEncoder : TestJSONEncoderSuper {
         }
     }
 
-    // Test the above `snprintf` edge case evaluation with a known triggering case
-    let knownBadDate = Date(timeIntervalSinceReferenceDate: 0.0021413276231263384)
-    localTestRoundTrip(of: TopLevelWrapper(knownBadDate))
+    // Test the above `snprintf` edge case evaluation with known triggering cases
+
+    // Tests the two precision digits larger case
+    let knownBadDateTwoExtraDigits = Date(timeIntervalSinceReferenceDate: 0.0021413276231263384)
+    localTestRoundTrip(of: TopLevelWrapper(knownBadDateTwoExtraDigits))
+
+    // Tests the one precision digit larger case
+    let knownBadDateOneExtraDigit = Date(timeIntervalSinceReferenceDate: 576487829.7193049)
+    localTestRoundTrip(of: TopLevelWrapper(knownBadDateOneExtraDigit))
 
     // We can't encode a top-level Date, so it'll be wrapped in a dictionary.
     localTestRoundTrip(of: TopLevelWrapper(Date()))