tests: make the offline tests aware of the current terminals row count (#2105)

This fixes the hideous output when your terminal would be too small to
hold all the threads.

common/util/string_util.cpp

@@ -0,0 +1,50 @@
+#include "string_util.h"
+
+#include <regex>
+
+namespace str_util {
+
+const std::string WHITESPACE = " \n\r\t\f\v";
+
+bool contains(const std::string& s, const std::string& substr) {
+  return s.find(substr) != std::string::npos;
+}
+
+bool starts_with(const std::string& s, const std::string& prefix) {
+  return s.rfind(prefix) == 0;
+}
+
+std::string ltrim(const std::string& s) {
+  size_t start = s.find_first_not_of(WHITESPACE);
+  return (start == std::string::npos) ? "" : s.substr(start);
+}
+
+std::string rtrim(const std::string& s) {
+  size_t end = s.find_last_not_of(WHITESPACE);
+  return (end == std::string::npos) ? "" : s.substr(0, end + 1);
+}
+
+std::string trim(const std::string& s) {
+  return rtrim(ltrim(s));
+}
+
+int line_count(const std::string& str) {
+  int result = 0;
+  for (auto& c : str) {
+    if (c == '\n') {
+      result++;
+    }
+  }
+  return result;
+}
+
+// NOTE - this won't work running within gk.exe!
+bool valid_regex(const std::string& regex) {
+  try {
+    std::regex re(regex);
+  } catch (const std::regex_error& e) {
+    return false;
+  }
+  return true;
+}
+}  // namespace str_util