[stdlib] Fix UnsafeBufferPointer range subscript getter tests (#3233)

All four of the Unsafe*BufferPointer range subscript getter tests (one for each range) were using the same test name string. This caused only one of the four tests to actually be registered to the test suite. This change fixes that issue, and adds a couple more tests for better coverage.

Author: austinzheng

validation-test/stdlib/UnsafeBufferPointer.swift.gyb

@@ -15,6 +15,8 @@ struct SubscriptGetTest {
   /// The values that should be expected by slicing the UBP, or `nil` if the
   /// test is expected to crash.
   let expectedValues: [Int]?
+  /// Same as `expectedValues`, but for closed ranges. `nil` if no difference.
+  let expectedClosedValues: [Int]?
   let loc: SourceLoc
 
   static var elementCount = (end - start)
@@ -35,10 +37,12 @@ struct SubscriptGetTest {
 
   init(
     rangeSelection: RangeSelection, expectedValues: [Int]? = nil,
+    expectedClosedValues: [Int]? = nil,
     file: String = #file, line: UInt = #line
   ) {
     self.rangeSelection = rangeSelection
     self.expectedValues = expectedValues
+    self.expectedClosedValues = expectedClosedValues ?? expectedValues
     self.loc = SourceLoc(file, line, comment: "test data")
   }
 }
@@ -48,8 +52,12 @@ let subscriptGetTests : [SubscriptGetTest] = [
   SubscriptGetTest(rangeSelection: .emptyRange, expectedValues: []),
 
   // Valid, edges.
-  SubscriptGetTest(rangeSelection: .leftEdge, expectedValues: [0]),
-  SubscriptGetTest(rangeSelection: .rightEdge, expectedValues: [19]),
+  SubscriptGetTest(rangeSelection: .leftEdge,
+    expectedValues: [],
+    expectedClosedValues: [0]),
+  SubscriptGetTest(rangeSelection: .rightEdge,
+    expectedValues: [],
+    expectedClosedValues: [19]),
 
   // Valid, internal.
   SubscriptGetTest(rangeSelection: .leftHalf, 
@@ -60,6 +68,12 @@ let subscriptGetTests : [SubscriptGetTest] = [
     expectedValues: [5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]),
   SubscriptGetTest(rangeSelection: .full,
     expectedValues: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]),
+  SubscriptGetTest(rangeSelection: .offsets(2, 4),
+    expectedValues: [2, 3],
+    expectedClosedValues: [2, 3, 4]),
+  SubscriptGetTest(rangeSelection: .offsets(16, 19),
+    expectedValues: [16, 17, 18],
+    expectedClosedValues: [16, 17, 18, 19]),
 
   // Invalid, bottom out of bounds.
   SubscriptGetTest(rangeSelection: .offsets(-1, -1)),
@@ -181,13 +195,17 @@ ${SelfName}TestSuite.test("badNilCount")
 }
 
 %   for RangeName in ['range', 'countableRange', 'closedRange', 'countableClosedRange']:
-${SelfName}TestSuite.test("subscript/get").forEach(in: subscriptGetTests) { 
+${SelfName}TestSuite.test("subscript/${RangeName}/get").forEach(in: subscriptGetTests) { 
   (test) in
 
+  let expectedValues: [Int]?
 %      if 'closed' in RangeName.lower():
   if test.rangeSelection.isEmpty {
     return
   }
+  expectedValues = test.expectedClosedValues
+%      else:
+  expectedValues = test.expectedValues
 %      end
 
   let elementCount = SubscriptGetTest.elementCount
@@ -198,10 +216,10 @@ ${SelfName}TestSuite.test("subscript/get").forEach(in: subscriptGetTests) {
 
   let range = test.rangeSelection.${RangeName}(in: buffer)
 
-  if test.expectedValues == nil { expectCrashLater() }
+  if expectedValues == nil { expectCrashLater() }
   let slice = buffer[range]
   expectEqual(
-    test.expectedValues!,
+    expectedValues!,
     slice.map { $0.value },
     stackTrace: SourceLocStack().with(test.loc)
   )