Index: libc/test/src/signal/sigprocmask_test.cpp
===================================================================
--- libc/test/src/signal/sigprocmask_test.cpp
+++ libc/test/src/signal/sigprocmask_test.cpp
@@ -14,6 +14,7 @@
 #include "src/signal/sigemptyset.h"
 #include "src/signal/sigprocmask.h"
 
+#include "utils/UnitTest/ErrnoSetterMatcher.h"
 #include "utils/UnitTest/Test.h"
 
 class SignalTest : public __llvm_libc::testing::Test {
@@ -27,28 +28,23 @@
   }
 };
 
+using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
+
 // This tests for invalid input.
 TEST_F(SignalTest, SigprocmaskInvalid) {
-  sigset_t valid;
-  // 17 and -4 are out of the range for sigprocmask's how paramater.
   llvmlibc_errno = 0;
-  EXPECT_EQ(__llvm_libc::sigprocmask(17, &valid, nullptr), -1);
-  EXPECT_EQ(llvmlibc_errno, EINVAL);
 
-  llvmlibc_errno = 0;
-  EXPECT_EQ(__llvm_libc::sigprocmask(-4, &valid, nullptr), -1);
-  EXPECT_EQ(llvmlibc_errno, EINVAL);
+  sigset_t valid;
+  // 17 and -4 are out of the range for sigprocmask's how paramater.
+  EXPECT_THAT(__llvm_libc::sigprocmask(17, &valid, nullptr), Fails(EINVAL));
+  EXPECT_THAT(__llvm_libc::sigprocmask(-4, &valid, nullptr), Fails(EINVAL));
 
   // This pointer is out of this processes address range.
   sigset_t *invalid = reinterpret_cast<sigset_t *>(-1);
-
-  llvmlibc_errno = 0;
-  EXPECT_EQ(__llvm_libc::sigprocmask(SIG_SETMASK, invalid, nullptr), -1);
-  EXPECT_EQ(llvmlibc_errno, EFAULT);
-
-  llvmlibc_errno = 0;
-  EXPECT_EQ(__llvm_libc::sigprocmask(-4, nullptr, invalid), -1);
-  EXPECT_EQ(llvmlibc_errno, EFAULT);
+  EXPECT_THAT(__llvm_libc::sigprocmask(SIG_SETMASK, invalid, nullptr),
+              Fails(EFAULT));
+  EXPECT_THAT(__llvm_libc::sigprocmask(-4, nullptr, invalid), Fails(EFAULT));
 }
 
 // This tests that when nothing is blocked, a process gets killed and alse tests
Index: libc/test/src/sys/mman/linux/mmap_test.cpp
===================================================================
--- libc/test/src/sys/mman/linux/mmap_test.cpp
+++ libc/test/src/sys/mman/linux/mmap_test.cpp
@@ -11,8 +11,12 @@
 #include "src/errno/llvmlibc_errno.h"
 #include "src/sys/mman/mmap.h"
 #include "src/sys/mman/munmap.h"
+#include "utils/UnitTest/ErrnoSetterMatcher.h"
 #include "utils/UnitTest/Test.h"
 
+using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
+
 TEST(MMapTest, NoError) {
   size_t alloc_size = 128;
   llvmlibc_errno = 0;
@@ -26,21 +30,14 @@
   // Since we used the MAP_ANONYMOUS flag, the contents of the newly
   // allocated memory should be initialized to zero.
   EXPECT_EQ(array[0], 0);
-
-  int ret_val = __llvm_libc::munmap(addr, alloc_size);
-  EXPECT_EQ(0, ret_val);
-  EXPECT_EQ(0, llvmlibc_errno);
+  EXPECT_THAT(__llvm_libc::munmap(addr, alloc_size), Succeeds());
 }
 
 TEST(MMapTest, Error_InvalidSize) {
   llvmlibc_errno = 0;
   void *addr = __llvm_libc::mmap(nullptr, 0, PROT_READ,
                                  MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
-  EXPECT_EQ(EINVAL, llvmlibc_errno);
-  EXPECT_EQ(addr, MAP_FAILED);
+  EXPECT_THAT(addr, Fails(EINVAL, MAP_FAILED));
 
-  llvmlibc_errno = 0;
-  int ret_val = __llvm_libc::munmap(0, 0);
-  EXPECT_EQ(-1, ret_val);
-  EXPECT_EQ(EINVAL, llvmlibc_errno);
+  EXPECT_THAT(__llvm_libc::munmap(0, 0), Fails(EINVAL));
 }
Index: libc/utils/testutils/StreamWrapper.cpp
===================================================================
--- libc/utils/testutils/StreamWrapper.cpp
+++ libc/utils/testutils/StreamWrapper.cpp
@@ -23,6 +23,7 @@
   return *this;
 }
 
+template StreamWrapper &StreamWrapper::operator<<<void *>(void *t);
 template StreamWrapper &StreamWrapper::operator<<<const char *>(const char *t);
 template StreamWrapper &StreamWrapper::operator<<<char *>(char *t);
 template StreamWrapper &StreamWrapper::operator<<<char>(char t);