Testing InputStreamLike with and without available member

test/Base_Tests/src/System/Input_Stream_Spec.enso

@@ -6,12 +6,33 @@ import Standard.Base.System.Input_Stream.Input_Stream
 from Standard.Test import all
 
 polyglot java import org.enso.base_test_helpers.RangeStream
+polyglot java import org.enso.base.Stream_Utils
 
 main filter=Nothing =
     suite = Test.build suite_builder->
         add_specs suite_builder
     suite.run_with_filter filter
 
+
+foreign js is_like data available = """
+    let at = 0
+    let is = {
+        read : function(arr, off, len) {
+          let cnt = 0;
+          while (len-- > 0) {
+            arr[off++] = data[at++];
+            cnt++;
+          }
+          return cnt;
+        }
+    }
+    if (available) {
+      is.available = function() {
+        return data.length - at;
+      };
+    }
+    return is;
+
 add_specs suite_builder = suite_builder.group "Input Stream" group_builder->
     group_builder.specify "should be peekable if backed by memory" <|
         Managed_Resource.bracket (Input_Stream.from_bytes [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]) (.close) stream->
@@ -61,3 +82,33 @@ add_specs suite_builder = suite_builder.group "Input Stream" group_builder->
         promoted_stream.peek_bytes 10 . should_equal [100, 101, 102, 103, 104]
         # The read still succeeds - ensuring there isn't some early EOF
         promoted_stream.read_n_bytes 10 . should_equal [100, 101, 102, 103, 104]
+
+    group_builder.specify "read without available" <|
+        stream_like = is_like [20, 5, 1, 10] False
+        is = Stream_Utils.asInputStream stream_like
+        is.available . should_equal 0
+
+        is.read . should_equal 20
+        is.read . should_equal 5
+
+        is.available . should_equal 0
+
+        is.read . should_equal 1
+        is.read . should_equal 10
+
+        is.available . should_equal 0
+
+    group_builder.specify "read with available" <|
+        stream_like = is_like [20, 6, 8, 23] True
+        is = Stream_Utils.asInputStream stream_like
+        is.available . should_equal 4
+
+        is.read . should_equal 20
+        is.read . should_equal 6
+
+        is.available . should_equal 2
+
+        is.read . should_equal 8
+        is.read . should_equal 23
+
+        is.available . should_equal 0