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diff --git a/indra/test/setenv.h b/indra/test/setenv.h
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+/**
+ * @file   setenv.h
+ * @author Nat Goodspeed
+ * @date   2020-04-01
+ * @brief  Provide a way for a particular test program to alter the
+ *         environment before entry to main().
+ * 
+ * $LicenseInfo:firstyear=2020&license=viewerlgpl$
+ * Copyright (c) 2020, Linden Research, Inc.
+ * $/LicenseInfo$
+ */
+
+#if ! defined(LL_SETENV_H)
+#define LL_SETENV_H
+
+#include <stdlib.h>                 // setenv()
+
+/**
+ * Our test.cpp main program responds to environment variables LOGTEST and
+ * LOGFAIL. But if you set (e.g.) LOGTEST=DEBUG before a viewer build, @em
+ * every test program in the build emits debug log output. This can be so
+ * voluminous as to slow down the build.
+ *
+ * With an integration test program, you can specifically build (e.g.) the
+ * INTEGRATION_TEST_llstring target, and set any environment variables you
+ * want for that. But with a unit test program, since executing the program is
+ * a side effect rather than an explicit target, specifically building (e.g.)
+ * PROJECT_lllogin_TEST_lllogin only builds the executable without running it.
+ *
+ * To set an environment variable for a particular test program, declare a
+ * static instance of SetEnv in its .cpp file. SetEnv's constructor takes
+ * pairs of strings, e.g.
+ *
+ * @code
+ * static SetEnv sLOGGING("LOGTEST", "INFO");
+ * @endcode
+ *
+ * Declaring a static instance of SetEnv is important because that ensures
+ * that the environment variables are set before main() is entered, since it
+ * is main() that examines LOGTEST and LOGFAIL.
+ */
+struct SetEnv
+{
+    // degenerate constructor, terminate recursion
+    SetEnv() {}
+
+    /**
+     * SetEnv() accepts an arbitrary number of pairs of strings: variable
+     * name, value, variable name, value ... Entering the constructor sets
+     * those variables in the process environment using Posix setenv(),
+     * overriding any previous value. If static SetEnv declarations in
+     * different translation units specify overlapping sets of variable names,
+     * it is indeterminate which instance will "win."
+     */
+    template <typename VAR, typename VAL, typename... ARGS>
+    SetEnv(VAR&& var, VAL&& val, ARGS&&... rest):
+        // constructor forwarding handles the tail of the list
+        SetEnv(std::forward<ARGS>(rest)...)
+    {
+        // set just the first (variable, value) pair
+        // 1 means override previous value if any
+        setenv(std::forward<VAR>(var), std::forward<VAL>(val), 1);
+    }
+};
+
+#endif /* ! defined(LL_SETENV_H) */