code: public ViewSelectionAssert hasAttributeEqualTo(String attributeName, Object expectedValue) {
          attribute(attributeName).containsOnly(expectedValue);
          return this;
      }
docs: Asserts that every view in the selection has an attribute with the given
  expected value. This is just a convenience shortcut for
  {@code attribute(attributeName).containsOnly(expectedValue)}.
  @param attributeName name of the attribute to check (e.g., {@code "text"}. The
  implementation will call a getter on each view based on this attribute name
  (e.g., {@code getText()}.
  @param expectedValue the expected value for the attribute
  @return self for chaining
  @throws AttributeAccessException if one of the views in the selection doesn't
  have a getter for the given attribute