Exploring -drawRect:

drawRectImpl

- (void)drawRect:(CGRect)rect {
  UIBezierPath *p = [[UIBezierPath alloc] init];
    
  CGPoint point = [_points objectAtIndex:0];
  [p moveToPoint:point];
  for (NSValue *v in _points) {
    point = [v CGPointValue];
    [p addLineToPoint:point];
  }
  
  [p setLineWidth:1.0f];
  [_lineColor setStroke];
  [p stroke];
}

error

Feb 13 10:09:17 Codemonkey.local Wealthfront[26532] <Error>: CGContextSaveGState: invalid context 0x0.
This is a serious error. This application, or a library it uses, is using an invalid context
and is thereby contributing to an overall degradation of system stability and reliability. 
This notice is a courtesy: please fix this problem. It will become a fatal error in an upcoming update.

firstTest

- (void)testDrawRect {
  WFLineChartView *v = [[WFLineChartView alloc] initWithFrame:CGRectMake(0, 0, 99.0f, 99.0f)];
  [v drawRect:v.bounds];
}

helpfulMacros.m

#define WFAssertPathElementMatchesElement(EXPECTED, ACTUAL) STAssertTrue([EXPECTED isEqual:ACTUAL], @"Element mismatch:\n%@\n%@", EXPECTED, ACTUAL)
#define WFAssertPathElementsMatchElements(EXPECTED, ACTUAL) \
({ \
  STAssertTrue([EXPECTED isKindOfClass:[NSArray class]], @"EXPECTED must be an NSArray: %@", EXPECTED); \
  STAssertTrue([ACTUAL isKindOfClass:[NSArray class]], @"ACTUAL must be an NSArray: %@", ACTUAL); \
  STAssertTrue(EXPECTED.count == ACTUAL.count, @"Wrong number of elements: %lu / %lu", (unsigned long)EXPECTED.count, (unsigned long)ACTUAL.count); \
  for (NSUInteger i=0; i < EXPECTED.count; i++) { \
    WFAssertPathElementMatchesElement([EXPECTED objectAtIndex:i], [ACTUAL objectAtIndex:i]); \
  } \
})

path

(lldb) po 0xe3bce30
<UIBezierPath: 0xe3bce30; <MoveTo {0, 84}>,
 <LineTo {11, 76.333328}>,
 <LineTo {22, 68.666672}>,
 <LineTo {33, 61}>,
 <LineTo {44, 53.333336}>,
 <LineTo {55, 45.666668}>,
 <LineTo {66, 38}>,
 <LineTo {77, 30.333336}>,
 <LineTo {88, 22.666668}>,
 <LineTo {99, 15}>,
 <LineTo {99, 99}>,
 <LineTo {0, 99}>,
 <LineTo {0, 84}>
(lldb) 

pathValidation

- (void)testDrawRect {
  /* (lldb) po 0xe3bce30
    <UIBezierPath: 0xe3bce30; <MoveTo {0, 84}>,
    <LineTo {11, 76.333328}>,
    <LineTo {22, 68.666672}>,
    <LineTo {33, 61}>,
    <LineTo {44, 53.333336}>,
    <LineTo {55, 45.666668}>,
    <LineTo {66, 38}>,
    <LineTo {77, 30.333336}>,
    <LineTo {88, 22.666668}>,
    <LineTo {99, 15}>,
    <LineTo {99, 99}>,
    <LineTo {0, 99}>,
    <LineTo {0, 84}>
    (lldb) 
  */
    NSArray *elements = [WFTestUtils createArrayOfElementsInPath:_paths[0]];
  NSArray *expectedElements = @[[WFCGPathElement pathElementWithType:kCGPathElementMoveToPoint
                                                              points:@[[NSValue valueWithCGPoint:CGPointMake(0.0f, 84.0f)]]],
                                [WFCGPathElement pathElementWithType:kCGPathElementAddLineToPoint
                                                              points:@[[NSValue valueWithCGPoint:CGPointMake(11.0f, 76.333328f)]]],
                                [WFCGPathElement pathElementWithType:kCGPathElementAddLineToPoint
                                                              points:@[[NSValue valueWithCGPoint:CGPointMake(22.0f, 68.666672f)]]],
                                [WFCGPathElement pathElementWithType:kCGPathElementAddLineToPoint
                                                              points:@[[NSValue valueWithCGPoint:CGPointMake(33.0f, 61.0f)]]],
                                [WFCGPathElement pathElementWithType:kCGPathElementAddLineToPoint
                                                              points:@[[NSValue valueWithCGPoint:CGPointMake(44.0f, 53.333336f)]]],
                                [WFCGPathElement pathElementWithType:kCGPathElementAddLineToPoint
                                                              points:@[[NSValue valueWithCGPoint:CGPointMake(55.0f, 45.666668f)]]],
                                [WFCGPathElement pathElementWithType:kCGPathElementAddLineToPoint
                                                              points:@[[NSValue valueWithCGPoint:CGPointMake(66.0f, 38.0f)]]],
                                [WFCGPathElement pathElementWithType:kCGPathElementAddLineToPoint
                                                              points:@[[NSValue valueWithCGPoint:CGPointMake(77.0f, 30.333336f)]]],
                                [WFCGPathElement pathElementWithType:kCGPathElementAddLineToPoint
                                                              points:@[[NSValue valueWithCGPoint:CGPointMake(88.0f, 22.666668f)]]],
                                [WFCGPathElement pathElementWithType:kCGPathElementAddLineToPoint
                                                              points:@[[NSValue valueWithCGPoint:CGPointMake(99.0f, 15.0f)]]],
                                [WFCGPathElement pathElementWithType:kCGPathElementAddLineToPoint
                                                              points:@[[NSValue valueWithCGPoint:CGPointMake(99.0f, 99.0f)]]],
                                [WFCGPathElement pathElementWithType:kCGPathElementAddLineToPoint
                                                              points:@[[NSValue valueWithCGPoint:CGPointMake(0.0f, 99.0f)]]],
                                [WFCGPathElement pathElementWithType:kCGPathElementAddLineToPoint
                                                              points:@[[NSValue valueWithCGPoint:CGPointMake(0.0f, 84.0f)]]],
                                ];
  WFAssertPathElementsMatchElements(expectedElements, elements);
}

shared

@implementation WFLineChartView

- (UIBezierPath *)createBezierPath {
  return [[UIBezierPath alloc] init];
}

@end

@implementation WFLineChartViewTest

- (UIBezierPath *)fakeCreatePath {
  UIBezierPath *p = [[UIBezierPath alloc] init];
  [_paths addObject:p];
  return p;
}

- (void)testDrawRect {
  WFLineChartView *v = [[WFLineChartView alloc] initWithFrame:CGRectMake(0, 0, 99.0f, 99.0f)];
  id mockV = [OCMockObject partialMockForObject:v];
  [[[mockV expect] andCall:@selector(fakeCreatePath) onObject:self] createBezierPath];
  [mockV verify];
}

@end

testPass

Test Suite 'WFLineChartViewTest' started at 2014-02-14 00:41:48 +0000
Test Case '-[WFLineChartViewTest testDrawRect]' started.
Test Case '-[WFLineChartViewTest testDrawRect]' passed (0.003 seconds).
Test Suite 'WFLineChartViewTest' finished at 2014-02-14 00:41:48 +0000.

testUtils

@interface WFCGPathElement : NSObject
@property(nonatomic, readonly) CGPathElementType type;
@property(nonatomic, readonly) NSArray *points;

- (instancetype)initWithElement:(const CGPathElement *)element;

@end

/**
 Iterate through the paths and create WFCGPathPoint objects.
 */
void WFCGPathApplierFunc(void *info, const CGPathElement *element) {
  NSMutableArray *points = (__bridge NSMutableArray *)info;
  WFCGPathElement *e = [[WFCGPathElement alloc] initWithElement:element];
  [points addObject:e];
}

@implementation WFTestUtils

+ (NSArray *)createArrayOfElementsInPath:(UIBezierPath *)path {
  NSMutableArray *points = [NSMutableArray new];
  CGPathRef cgp = path.CGPath;
  CGPathApply(cgp, (__bridge void *)(points), WFCGPathApplierFunc);
  return points;
}

@end

withContext

- (void)testDrawRect {
  WFLineChartView *v = [[WFLineChartView alloc] initWithFrame:CGRectMake(0, 0, 99.0f, 99.0f)];
   CGFloat scaleFactor = [[UIScreen mainScreen] scale];
  CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
  CGRect bounds = view.bounds;
  CGContextRef context = CGBitmapContextCreate(NULL,
                                               bounds.size.width * scaleFactor,
                                               bounds.size.height * scaleFactor,
                                               8,
                                               bounds.size.width * scaleFactor * 4,
                                               colorSpace,
                                               (CGBitmapInfo)kCGImageAlphaPremultipliedFirst);
  UIGraphicsPushContext(context);
  [view drawRect:bounds];
  UIGraphicsPopContext();
  CFRelease(colorSpace);
  CFRelease(context);
}