Add more tests for std::string on all platforms

source/stdcpp/test/string.d

@@ -23,5 +23,22 @@ unittest
     a.push_back('a');
     assert(a.size() == 6);
     // verifying small string optimization, this is 15 on GCC, 22-23 on clang
-    assert(a.capacity == stringCapacity("hello"));
+    assert(a.capacity == stringCapacity("helloa"));
+    assert(a.front() == 'h');
+    assert(a.back() == 'a');
+    a.resize(4); // shrinks a to "hell"
+    assert(a.size() == 4);
+    immutable LongStr = "Hi, this is a test for string capacity growth for a length more than the base SSO";
+    auto b = std_string(LongStr);
+    assert(b.capacity == stringCapacity(LongStr.ptr));
+    a.swap(b); // a and b swaps
+    assert(a.capacity == stringCapacity(LongStr.ptr));
+    assert(b.capacity == stringCapacity("hell")); // a was shrinked to hell so b contains 'hell'
+    b.pop_back();
+    assert(b.size() == 3);
+    assert(b[0] == 'h');
+    assert(b[1] == 'e');
+    assert(a.empty == 0);
+    a.clear();
+    assert(a.empty == 1);
 }