Add comments explaining tests

Author: smowton

go/ql/test/library-tests/semmle/go/aliases/DataflowFields/embedding.go

@@ -5,6 +5,8 @@ import (
 	"test.com/basename/pkg2"
 )
 
+// Tests that dataflow behaves as expected when loads and stores from a field traverse embeddings that use different type names.
+
 // pkg2.IntStruct is an alias for pkg1.IntStruct
 // Note trickery with packages is necessary so that Go will assign the fields the same name as well as the same type.
 

go/ql/test/library-tests/semmle/go/aliases/DataflowFields/simple.go

@@ -1,5 +1,8 @@
 package test
 
+// Tests that dataflow behaves as expected when field loads and stores, and pointer accesses, go via
+// types which are identical, but which use different aliases.
+
 func source() int    { return 0 }
 func sink(value int) {}
 

go/ql/test/library-tests/semmle/go/aliases/InterfaceImpls/test.go

@@ -1,5 +1,8 @@
 package intfs
 
+// Tests that dataflow and interface implementation behave as expected when an interface
+// is implemented using a non-equal but identical type, i.e. an equal type after alias resolution.
+
 type IntAlias = int
 
 type Target = interface {

go/ql/test/library-tests/semmle/go/aliases/MethodDefs/methods.go

@@ -1,5 +1,7 @@
 package aliases
 
+// Tests how interfaces defining identical types are represented in the database.
+
 type IntAlias = int
 
 type S1 = struct{ x int }

go/ql/test/library-tests/semmle/go/aliases/defsuses/defsuses.go

@@ -1,5 +1,8 @@
 package aliases
 
+// Tests how defs and uses of fields are represented in the database
+// when identical types are used.
+
 type IntAlias = int
 
 type S1 = struct{ x int }