diff --git a/tests/snippets/membership.py b/tests/snippets/membership.py
index a944c45398..2987c3c0fe 100644
--- a/tests/snippets/membership.py
+++ b/tests/snippets/membership.py
@@ -12,9 +12,8 @@
 assert "whatever" not in "foobar"
 
 # test bytes
-# TODO: uncomment this when bytes are implemented
-# assert b"foo" in b"foobar"
-# assert b"whatever" not in b"foobar"
+assert b"foo" in b"foobar"
+assert b"whatever" not in b"foobar"
 assert b"1" < b"2"
 assert b"1" <= b"2"
 assert b"5" <= b"5"
@@ -32,18 +31,20 @@
 assert 3 not in set([1, 2])
 
 # test dicts
-# TODO: test dicts when keys other than strings will be allowed
 assert "a" in {"a": 0, "b": 0}
 assert "c" not in {"a": 0, "b": 0}
+assert 1 in {1: 5, 7: 12}
+assert 5 not in {9: 10, 50: 100}
+assert True in {True: 5}
+assert False not in {True: 5}
 
 # test iter
 assert 3 in iter([1, 2, 3])
 assert 3 not in iter([1, 2])
 
 # test sequence
-# TODO: uncomment this when ranges are usable
-# assert 1 in range(0, 2)
-# assert 3 not in range(0, 2)
+assert 1 in range(0, 2)
+assert 3 not in range(0, 2)
 
 # test __contains__ in user objects
 class MyNotContainingClass():
diff --git a/tests/snippets/strings.py b/tests/snippets/strings.py
index 0baa35d23c..28df3f47f4 100644
--- a/tests/snippets/strings.py
+++ b/tests/snippets/strings.py
@@ -29,6 +29,14 @@
 
 assert str(["a", "b", "can't"]) == "['a', 'b', \"can't\"]"
 
+assert "xy" * 3 == "xyxyxy"
+assert "x" * 0 == ""
+assert "x" * -1 == ""
+
+assert 3 * "xy" == "xyxyxy"
+assert 0 * "x" == ""
+assert -1 * "x" == ""
+
 a = 'Hallo'
 assert a.lower() == 'hallo'
 assert a.upper() == 'HALLO'
@@ -94,6 +102,7 @@
 ]
 
 
+# requires CPython 3.7, and the CI currently runs with 3.6
 # assert c.isascii()
 assert c.index('a') == 1
 assert c.rindex('l') == 3
diff --git a/vm/src/obj/objstr.rs b/vm/src/obj/objstr.rs
index 22eda1f34b..e5e2afe370 100644
--- a/vm/src/obj/objstr.rs
+++ b/vm/src/obj/objstr.rs
@@ -183,7 +183,12 @@ impl PyString {
         if objtype::isinstance(&val, &vm.ctx.int_type()) {
             let value = &self.value;
             let multiplier = objint::get_value(&val).to_i32().unwrap();
-            let mut result = String::new();
+            let capacity = if multiplier > 0 {
+                multiplier.to_usize().unwrap() * value.len()
+            } else {
+                0
+            };
+            let mut result = String::with_capacity(capacity);
             for _x in 0..multiplier {
                 result.push_str(value.as_str());
             }
@@ -193,6 +198,11 @@ impl PyString {
         }
     }
 
+    #[pymethod(name = "__rmul__")]
+    fn rmul(&self, val: PyObjectRef, vm: &VirtualMachine) -> PyResult<String> {
+        self.mul(val, vm)
+    }
+
     #[pymethod(name = "__str__")]
     fn str(zelf: PyRef<Self>, _vm: &VirtualMachine) -> PyStringRef {
         zelf
@@ -206,7 +216,7 @@ impl PyString {
         } else {
             '\''
         };
-        let mut formatted = String::new();
+        let mut formatted = String::with_capacity(value.len());
         formatted.push(quote_char);
         for c in value.chars() {
             if c == quote_char || c == '\\' {
@@ -799,7 +809,7 @@ impl PyString {
     #[pymethod]
     fn expandtabs(&self, tab_stop: OptionalArg<usize>, _vm: &VirtualMachine) -> String {
         let tab_stop = tab_stop.into_option().unwrap_or(8 as usize);
-        let mut expanded_str = String::new();
+        let mut expanded_str = String::with_capacity(self.value.len());
         let mut tab_size = tab_stop;
         let mut col_count = 0 as usize;
         for ch in self.value.chars() {