diff --git a/Tests/opal/CGContext/TestInfo b/Tests/opal/CGContext/TestInfo
new file mode 100644
index 0000000..e69de29
diff --git a/Tests/opal/CGContext/gstate.m b/Tests/opal/CGContext/gstate.m
new file mode 100644
index 0000000..555dac7
--- /dev/null
+++ b/Tests/opal/CGContext/gstate.m
@@ -0,0 +1,101 @@
+/* CGContext graphics state: the CTM of a bitmap context, transforms,
+   save/restore, clipping and global alpha.  Expected values checked against
+   Apple CoreGraphics on a macOS runner. */
+#include "Testing.h"
+
+#include <CoreGraphics/CGContext.h>
+#include <CoreGraphics/CGBitmapContext.h>
+#include <CoreGraphics/CGImage.h>
+#include <CoreGraphics/CGColorSpace.h>
+#include <CoreGraphics/CGColor.h>
+#include <CoreGraphics/CGAffineTransform.h>
+#include <math.h>
+#include <stdlib.h>
+
+static BOOL eqf(CGFloat a, CGFloat b)
+{
+  CGFloat d = a - b;
+  if (d < 0) d = -d;
+  return d < 1e-4;
+}
+
+static BOOL teq(CGAffineTransform t, CGFloat a, CGFloat b, CGFloat c,
+                CGFloat d, CGFloat tx, CGFloat ty)
+{
+  return eqf(t.a, a) && eqf(t.b, b) && eqf(t.c, c) && eqf(t.d, d)
+      && eqf(t.tx, tx) && eqf(t.ty, ty);
+}
+
+static CGContextRef makeCtx(CGColorSpaceRef dev, unsigned char **data)
+{
+  *data = calloc(10 * 10 * 4, 1);
+  return CGBitmapContextCreate(*data, 10, 10, 8, 40, dev,
+    kCGImageAlphaPremultipliedLast);
+}
+
+int main(void)
+{
+  CGColorSpaceRef dev = CGColorSpaceCreateDeviceRGB();
+
+  START_SET("CGContext")
+
+  unsigned char *data;
+  CGContextRef ctx = makeCtx(dev, &data);
+
+  PASS(teq(CGContextGetCTM(ctx), 1, 0, 0, 1, 0, 0),
+       "the initial CTM of a bitmap context is the identity");
+  CGContextTranslateCTM(ctx, 2, 3);
+  PASS(teq(CGContextGetCTM(ctx), 1, 0, 0, 1, 2, 3),
+       "translating the CTM moves the origin");
+  CGContextScaleCTM(ctx, 2, 2);
+  PASS(teq(CGContextGetCTM(ctx), 2, 0, 0, 2, 2, 3),
+       "scaling the CTM scales the diagonal and keeps the translation");
+
+  CGContextSaveGState(ctx);
+  CGContextTranslateCTM(ctx, 100, 100);
+  CGContextRestoreGState(ctx);
+  PASS(teq(CGContextGetCTM(ctx), 2, 0, 0, 2, 2, 3),
+       "restoring the graphics state restores the CTM");
+
+  /* Clip confines a fill to the clip rect. */
+  unsigned char *cdata;
+  CGContextRef cctx = makeCtx(dev, &cdata);
+  CGFloat green[] = {0, 1, 0, 1};
+  CGColorRef gc = CGColorCreate(dev, green);
+  CGContextSetFillColorWithColor(cctx, gc);
+  CGContextClipToRect(cctx, CGRectMake(2, 2, 4, 4));
+  CGContextFillRect(cctx, CGRectMake(0, 0, 10, 10));
+  unsigned char *cd = (unsigned char *)CGBitmapContextGetData(cctx);
+  int inC = (4 * 10 + 4) * 4, outC = 0;
+  PASS(cd[inC] == 0 && cd[inC+1] == 255 && cd[inC+2] == 0 && cd[inC+3] == 255,
+       "a pixel inside the clip rect is filled");
+  PASS(cd[outC] == 0 && cd[outC+1] == 0 && cd[outC+2] == 0 && cd[outC+3] == 0,
+       "a pixel outside the clip rect is untouched");
+
+  /* Global alpha scales the fill's coverage. */
+  unsigned char *adata;
+  CGContextRef actx = makeCtx(dev, &adata);
+  CGFloat red[] = {1, 0, 0, 1};
+  CGColorRef rc = CGColorCreate(dev, red);
+  CGContextSetAlpha(actx, 0.5);
+  CGContextSetFillColorWithColor(actx, rc);
+  CGContextFillRect(actx, CGRectMake(0, 0, 10, 10));
+  unsigned char *ad = (unsigned char *)CGBitmapContextGetData(actx);
+  PASS(abs((int)ad[0] - 128) <= 1 && ad[1] == 0 && ad[2] == 0
+       && abs((int)ad[3] - 128) <= 1,
+       "a global alpha of one half premultiplies the fill");
+
+  CGColorRelease(gc);
+  CGColorRelease(rc);
+  CGContextRelease(ctx);
+  CGContextRelease(cctx);
+  CGContextRelease(actx);
+  free(data);
+  free(cdata);
+  free(adata);
+
+  END_SET("CGContext")
+
+  CGColorSpaceRelease(dev);
+  return 0;
+}