diff --git a/simgear/misc/test_macros.hxx b/simgear/misc/test_macros.hxx
index c063dc3a..0ba80616 100644
--- a/simgear/misc/test_macros.hxx
+++ b/simgear/misc/test_macros.hxx
@@ -1,3 +1,5 @@
+// -*- coding: utf-8 -*-
+
 #ifndef SG_MISC_TEST_MACROS_HXX
 #define SG_MISC_TEST_MACROS_HXX
 
@@ -5,6 +7,7 @@
 #include <cmath>                // for std::fabs()
 
 
+// Assertion-like test
 #define SG_VERIFY(a) \
     if (!(a))  { \
         std::cerr << "failed: " << #a << std::endl; \
@@ -12,70 +15,163 @@
         exit(1); \
     }
 
-#define SG_CHECK_EQUAL(a, b) \
+// Internal macro (implementation detail). 'a' and 'b' don't always support
+// operator<<. This is why we use (a0) and (b0) after '<<', otherwise in such
+// cases the test couldn't be compiled, even if 'stream' is false.
+#define SG_CHECK_EQUAL0(a, b, stream, a0, b0) \
     if ( !((a) == (b)) )  { \
         std::cerr << "failed: " << #a << " == " << #b << std::endl; \
-        std::cerr << "\tgot '" << (a) << "' and '" << (b) << "'" << std::endl; \
+        if (stream) { \
+          std::cerr << "\tgot '" << (a0) << "' and '" << (b0) << "'" \
+                    << std::endl; \
+        }; \
         std::cerr << "\tat " << __FILE__ << ":" << __LINE__ << std::endl; \
         exit(1); \
     }
 
-#define SG_CHECK_EQUAL_EP(a, b) \
+// Test macros for user consumption. The _NOSTREAM variant is for cases where
+// 'a' or 'b' doesn't support operator<< (or where using it would have
+// undesirable side effects).
+#define SG_CHECK_EQUAL(a, b) SG_CHECK_EQUAL0((a), (b), true, (a), (b))
+#define SG_CHECK_EQUAL_NOSTREAM(a, b) SG_CHECK_EQUAL0((a), (b), false, "", "")
+
+// “Approximate equality” test (EP stands for “epsilon”)
+#define SG_CHECK_EQUAL_EP0(a, b, stream, a0, b0) \
     if (std::fabs((a) - (b)) > SG_EPSILON)  { \
         std::cerr << "failed: " << #a << " ~= " << #b << std::endl; \
-        std::cerr << "\tgot '" << (a) << "' and '" << (b) << "'" << std::endl; \
+        if (stream) { \
+          std::cerr << "\tgot '" << (a0) << "' and '" << (b0) << "'" \
+                    << std::endl; \
+        }; \
+        std::cerr << "\tat " << __FILE__ << ":" << __LINE__ << std::endl; \
+        exit(1); \
+    }
+
+#define SG_CHECK_EQUAL_EP(a, b) SG_CHECK_EQUAL_EP0((a), (b), true, (a), (b))
+#define SG_CHECK_EQUAL_EP_NOSTREAM(a, b) \
+    SG_CHECK_EQUAL_EP0((a), (b), false, "", "")
+
+// Same as SG_CHECK_EQUAL_EP*, except the “epsilon” can be chosen by the caller
+#define SG_CHECK_EQUAL_EP2_0(a, b, ep, stream, a0, b0) \
+  if (std::fabs((a) - (b)) > (ep))  {                  \
+        std::cerr << "failed: " << #a << " ~= " << #b << std::endl; \
+        if (stream) { \
+          std::cerr << "\tgot '" << (a0) << "' and '" << (b0) << "'" \
+                    << std::endl; \
+        }; \
         std::cerr << "\tat " << __FILE__ << ":" << __LINE__ << std::endl; \
         exit(1); \
     }
 
 #define SG_CHECK_EQUAL_EP2(a, b, ep) \
-  if (std::fabs((a) - (b)) > (ep))  {                               \
-        std::cerr << "failed: " << #a << " ~= " << #b << std::endl; \
-        std::cerr << "\tgot '" << (a) << "' and '" << (b) << "'" << std::endl; \
-        std::cerr << "\tat " << __FILE__ << ":" << __LINE__ << std::endl; \
-        exit(1); \
-    }
+    SG_CHECK_EQUAL_EP2_0((a), (b), ep, true, (a), (b))
+#define SG_CHECK_EQUAL_EP2_NOSTREAM(a, b) \
+    SG_CHECK_EQUAL_EP2_0((a), (b), ep, false, "", "")
 
-#define SG_CHECK_NE(a, b) \
+// “Non-equal” test
+#define SG_CHECK_NE0(a, b, stream, a0, b0) \
     if ( !((a) != (b)) )  { \
         std::cerr << "failed: " << #a << " != " << #b << std::endl; \
-        std::cerr << "\tgot '" << (a) << "' and '" << (b) << "'" << std::endl; \
+        if (stream) { \
+          std::cerr << "\tgot '" << (a0) << "' and '" << (b0) << "'" \
+                    << std::endl; \
+        }; \
         std::cerr << "\tat " << __FILE__ << ":" << __LINE__ << std::endl; \
         exit(1); \
     }
 
-#define SG_CHECK_LT(a, b) \
+#define SG_CHECK_NE(a, b) SG_CHECK_NE0((a), (b), true, (a), (b))
+#define SG_CHECK_NE_NOSTREAM(a, b) SG_CHECK_NE0((a), (b), false, "", "")
+
+// “Lower than” test
+#define SG_CHECK_LT0(a, b, stream, a0, b0) \
     if ( !((a) < (b)) )  { \
         std::cerr << "failed: " << #a << " < " << #b << std::endl; \
-        std::cerr << "\tgot '" << (a) << "' and '" << (b) << "'" << std::endl; \
+        if (stream) { \
+          std::cerr << "\tgot '" << (a0) << "' and '" << (b0) << "'" \
+                    << std::endl; \
+        }; \
         std::cerr << "\tat " << __FILE__ << ":" << __LINE__ << std::endl; \
         exit(1); \
     }
 
-#define SG_CHECK_LE(a, b) \
+#define SG_CHECK_LT(a, b) SG_CHECK_LT0((a), (b), true, (a), (b))
+#define SG_CHECK_LT_NOSTREAM(a, b) SG_CHECK_LT0((a), (b), false, "", "")
+
+// “Lower than or equal” test
+#define SG_CHECK_LE0(a, b, stream, a0, b0) \
     if ( !((a) <= (b)) )  { \
         std::cerr << "failed: " << #a << " <= " << #b << std::endl; \
-        std::cerr << "\tgot '" << (a) << "' and '" << (b) << "'" << std::endl; \
+        if (stream) { \
+          std::cerr << "\tgot '" << (a0) << "' and '" << (b0) << "'" \
+                    << std::endl; \
+        }; \
         std::cerr << "\tat " << __FILE__ << ":" << __LINE__ << std::endl; \
         exit(1); \
     }
 
-#define SG_CHECK_GT(a, b) \
+#define SG_CHECK_LE(a, b) SG_CHECK_LE0((a), (b), true, (a), (b))
+#define SG_CHECK_LE_NOSTREAM(a, b) SG_CHECK_LE0((a), (b), false, "", "")
+
+// “Greater than” test
+#define SG_CHECK_GT0(a, b, stream, a0, b0) \
     if ( !((a) > (b)) )  { \
         std::cerr << "failed: " << #a << " > " << #b << std::endl; \
-        std::cerr << "\tgot '" << (a) << "' and '" << (b) << "'" << std::endl; \
+        if (stream) { \
+          std::cerr << "\tgot '" << (a0) << "' and '" << (b0) << "'" \
+                    << std::endl; \
+        }; \
         std::cerr << "\tat " << __FILE__ << ":" << __LINE__ << std::endl; \
         exit(1); \
     }
 
-#define SG_CHECK_GE(a, b) \
+#define SG_CHECK_GT(a, b) SG_CHECK_GT0((a), (b), true, (a), (b))
+#define SG_CHECK_GT_NOSTREAM(a, b) SG_CHECK_GT0((a), (b), false, "", "")
+
+// “Greater than or equal” test
+#define SG_CHECK_GE0(a, b, stream, a0, b0) \
     if ( !((a) >= (b)) )  { \
         std::cerr << "failed: " << #a << " >= " << #b << std::endl; \
-        std::cerr << "\tgot '" << (a) << "' and '" << (b) << "'" << std::endl; \
+        if (stream) { \
+          std::cerr << "\tgot '" << (a0) << "' and '" << (b0) << "'" \
+                    << std::endl; \
+        }; \
         std::cerr << "\tat " << __FILE__ << ":" << __LINE__ << std::endl; \
         exit(1); \
     }
 
+#define SG_CHECK_GE(a, b) SG_CHECK_GE0((a), (b), true, (a), (b))
+#define SG_CHECK_GE_NOSTREAM(a, b) SG_CHECK_GE0((a), (b), false, "", "")
+
+// “Is NULL” test
+#define SG_CHECK_IS_NULL0(a, stream, a0) \
+    if ( !((a) == nullptr) )  { \
+        std::cerr << "failed: " << #a << " == nullptr" << std::endl; \
+        if (stream) { \
+          std::cerr << "\tgot '" << (a0) << "'" << std::endl; \
+        }; \
+        std::cerr << "\tat " << __FILE__ << ":" << __LINE__ << std::endl; \
+        exit(1); \
+    }
+
+#define SG_CHECK_IS_NULL(a) SG_CHECK_IS_NULL0((a), true, (a))
+#define SG_CHECK_IS_NULL_NOSTREAM(a) SG_CHECK_IS_NULL0((a), false, "")
+
+// “Is not NULL” test
+#define SG_CHECK_IS_NOT_NULL0(a, stream, a0) \
+    if ( !((a) != nullptr) )  { \
+        std::cerr << "failed: " << #a << " != nullptr" << std::endl; \
+        if (stream) { \
+          std::cerr << "\tgot '" << (a0) << "'" << std::endl; \
+        }; \
+        std::cerr << "\tat " << __FILE__ << ":" << __LINE__ << std::endl; \
+        exit(1); \
+    }
+
+#define SG_CHECK_IS_NOT_NULL(a) SG_CHECK_IS_NOT_NULL0((a), true, (a))
+#define SG_CHECK_IS_NOT_NULL_NOSTREAM(a) SG_CHECK_IS_NOT_NULL0((a), false, "")
+
+// “Always failing” test
 #define SG_TEST_FAIL(msg) \
   std::cerr << "failure: " << msg; \
   exit(1);