Add an optional offset to File.readBytes().

test/io/file/read_bytes.wren

@@ -10,4 +10,10 @@ System.print(file.readBytes(7)) // expect: this is
 // Allows zero.
 System.print(file.readBytes(0).bytes.count) // expect: 0
 
+// A longer number reads the whole file.
+System.print(file.readBytes(100)) // expect: this is a text file
+
+// Reading past the end truncates the buffer.
+System.print(file.readBytes(100).bytes.count) // expect: 19
+
 file.close()

test/io/file/read_bytes_from.wren

@@ -0,0 +1,20 @@
+import "io" for File
+
+var file = File.open("test/io/file/file.txt")
+
+// Zero starts at the beginning.
+System.print(file.readBytes(3, 0)) // expect: thi
+
+// Starts at the offset.
+System.print(file.readBytes(8, 3)) // expect: s is a t
+
+// Allows zero.
+System.print(file.readBytes(0, 4).bytes.count) // expect: 0
+
+// A longer number length reads until the end.
+System.print(file.readBytes(100, 2)) // expect: is is a text file
+
+// An offset past the end returns an empty string.
+System.print(file.readBytes(100, 30).bytes.count) // expect: 0
+
+file.close()

test/io/file/read_bytes_from_after_close.wren

@@ -0,0 +1,6 @@
+import "io" for File
+
+var file = File.open("test/io/file/file.txt")
+file.close()
+
+file.readBytes(3, 0) // expect runtime error: File is not open.

test/io/file/read_bytes_from_count_negative.wren

@@ -0,0 +1,4 @@
+import "io" for File
+
+var file = File.open("test/io/file/file.txt")
+file.readBytes(-1, 0) // expect runtime error: Count cannot be negative.

test/io/file/read_bytes_from_count_not_integer.wren

@@ -0,0 +1,4 @@
+import "io" for File
+
+var file = File.open("test/io/file/file.txt")
+file.readBytes(1.2, 0) // expect runtime error: Count must be an integer.

test/io/file/read_bytes_from_count_not_num.wren

@@ -0,0 +1,4 @@
+import "io" for File
+
+var file = File.open("test/io/file/file.txt")
+file.readBytes("not num", 0) // expect runtime error: Count must be an integer.

test/io/file/read_bytes_from_offset_negative.wren

@@ -0,0 +1,4 @@
+import "io" for File
+
+var file = File.open("test/io/file/file.txt")
+file.readBytes(1, -1) // expect runtime error: Offset cannot be negative.

test/io/file/read_bytes_from_offset_not_integer.wren

@@ -0,0 +1,4 @@
+import "io" for File
+
+var file = File.open("test/io/file/file.txt")
+file.readBytes(1, 1.2) // expect runtime error: Offset must be an integer.

test/io/file/read_bytes_from_offset_not_num.wren

@@ -0,0 +1,4 @@
+import "io" for File
+
+var file = File.open("test/io/file/file.txt")
+file.readBytes(1, "not num") // expect runtime error: Offset must be an integer.