diff --git a/vlib/compiler/main.v b/vlib/compiler/main.v
index 79a5734ec1..582fb04704 100644
--- a/vlib/compiler/main.v
+++ b/vlib/compiler/main.v
@@ -506,23 +506,21 @@ pub fn (v mut V) generate_main() {
 			if v.table.main_exists() {
 				verror('test files cannot have function `main`')
 			}
-			if !v.table.has_at_least_one_test_fn() {
+			test_fn_names := v.table.all_test_function_names()
+			if test_fn_names.len == 0 {
 				verror('test files need to have at least one test function')
 			}
+			
 			// Generate a C `main`, which calls every single test function
 			v.gen_main_start(false)
 
 			if v.pref.is_stats {
 				cgen.genln('BenchedTests bt = main__start_testing();')
 			}
-
-			for _, f in v.table.fns {
-				if f.name.starts_with('main__test_') {
-					if v.pref.is_stats {
-						cgen.genln('BenchedTests_testing_step_start(&bt, tos3("$f.name"));') }
-					cgen.genln('$f.name ();')
-					if v.pref.is_stats { cgen.genln('BenchedTests_testing_step_end(&bt);') }
-				}
+			for tfname in test_fn_names {
+				if v.pref.is_stats { cgen.genln('BenchedTests_testing_step_start(&bt, tos3("$tfname"));') }
+				cgen.genln('$tfname ();')
+				if v.pref.is_stats { cgen.genln('BenchedTests_testing_step_end(&bt);') }
 			}
 			if v.pref.is_stats { cgen.genln('BenchedTests_end_testing(&bt);') }
 			v.gen_main_end('return g_test_fails > 0')
@@ -766,17 +764,25 @@ pub fn (v &V)  get_user_files() []string {
 		user_files << filepath.join(preludes_path,'tests_with_stats.v')
 	}
 
-	// v volt/slack_test.v: compile all .v files to get the environment
-	// I need to implement user packages! TODO
-	is_test_with_imports := dir.ends_with('_test.v') &&
-		(dir.contains('${os.path_separator}volt') ||
-		dir.contains('${os.path_separator}c2volt'))// TODO
-	if is_test_with_imports {
-		user_files << dir
-		if pos := dir.last_index(os.path_separator) {
-			dir = dir[..pos] + os.path_separator// TODO why is this needed
+	is_test := dir.ends_with('_test.v')
+	mut is_internal_module_test := false
+	if is_test {
+		tcontent := os.read_file( dir ) or { panic('$dir does not exist') }
+		if tcontent.contains('module ') && !tcontent.contains('module main') {
+			is_internal_module_test = true
 		}
 	}
+	if is_internal_module_test {
+		// v volt/slack_test.v: compile all .v files to get the environment
+		single_test_v_file := os.realpath(dir)
+		if v.pref.is_verbose {
+			v.log('> Compiling an internal module _test.v file $single_test_v_file .')
+			v.log('> That brings in all other ordinary .v files in the same module too .')
+		}
+		user_files << single_test_v_file
+		dir = os.basedir( single_test_v_file )
+	}
+	
 	if dir.ends_with('.v') || dir.ends_with('.vsh') {
 		single_v_file := dir
 		// Just compile one file and get parent dir
diff --git a/vlib/compiler/preludes/tests_assertions.v b/vlib/compiler/preludes/tests_assertions.v
index 306145f488..d1688715a6 100644
--- a/vlib/compiler/preludes/tests_assertions.v
+++ b/vlib/compiler/preludes/tests_assertions.v
@@ -19,7 +19,7 @@ fn cb_assertion_failed(filename string, line int, sourceline string, funcname st
 		else { true }
 	}
 	final_filename := if use_relative_paths { filename } else { os.realpath( filename ) }
-	final_funcname := funcname.replace('main__','')
+	final_funcname := funcname.replace('main__','').replace('__','.')
 
 	mut fail_message := 'FAILED assertion'
 	if color_on { fail_message = term.bold(term.red(fail_message)) }
diff --git a/vlib/compiler/preludes/tests_with_stats.v b/vlib/compiler/preludes/tests_with_stats.v
index daf9597b73..2440d66b58 100644
--- a/vlib/compiler/preludes/tests_with_stats.v
+++ b/vlib/compiler/preludes/tests_with_stats.v
@@ -34,7 +34,7 @@ fn start_testing() BenchedTests {
 
 // Called before each test_ function, defined in file_test.v
 fn (b mut BenchedTests) testing_step_start(stepfunc string) {
-	b.step_func_name = stepfunc.replace('main__','')
+	b.step_func_name = stepfunc.replace('main__','').replace('__','.')
 	b.oks   = C.g_test_oks
 	b.fails = C.g_test_fails
 	b.bench.step()
diff --git a/vlib/compiler/table.v b/vlib/compiler/table.v
index 36932a9d37..fa39d0493e 100644
--- a/vlib/compiler/table.v
+++ b/vlib/compiler/table.v
@@ -778,13 +778,14 @@ fn (t &Table) main_exists() bool {
 	return false
 }
 
-fn (t &Table) has_at_least_one_test_fn() bool {
+fn (t &Table) all_test_function_names() []string {
+	mut res := []string
 	for _, f in t.fns {
-		if f.name.starts_with('main__test_') {
-			return true
+		if f.name.contains('__test_') {
+			res << f.name
 		}
 	}
-	return false
+	return res
 }
 
 fn (t &Table) find_const(name string) ?Var {
diff --git a/vlib/compiler/tests/modules/amodule/another_internal_module_test.v b/vlib/compiler/tests/modules/amodule/another_internal_module_test.v
new file mode 100644
index 0000000000..06fd3951ac
--- /dev/null
+++ b/vlib/compiler/tests/modules/amodule/another_internal_module_test.v
@@ -0,0 +1,16 @@
+module amodule
+
+// This tests whether _test.v files can be *internal* to a 
+// module, and thus have access to its guts.
+
+// NB: the function test_private_isub() is defined both here
+// and inside internal_module_test.v . That is done on purpose, 
+// with the goal of ensuring that _test.v files are compiled 
+// *independently* from each other.
+//
+// _test.v files should *only* import all the other normal .v 
+// files from the same folder, NOT other _test.v files from it.
+
+fn test_private_isub(){
+  assert private_isub(7,5) == 2
+}
diff --git a/vlib/compiler/tests/modules/amodule/internal_module_test.v b/vlib/compiler/tests/modules/amodule/internal_module_test.v
new file mode 100644
index 0000000000..2064895007
--- /dev/null
+++ b/vlib/compiler/tests/modules/amodule/internal_module_test.v
@@ -0,0 +1,16 @@
+module amodule
+
+// this tests whether _test.v files can be *internal* 
+// to a module, and thus have access to its guts.
+
+fn test_iadd(){
+	assert iadd(10, 20) == 30
+}
+
+fn test_imul(){
+	assert imul(5,8) == 40
+}
+
+fn test_private_isub(){
+  assert private_isub(10,6) == 4
+}
diff --git a/vlib/compiler/tests/modules/amodule/module.v b/vlib/compiler/tests/modules/amodule/module.v
new file mode 100644
index 0000000000..f2742b4e73
--- /dev/null
+++ b/vlib/compiler/tests/modules/amodule/module.v
@@ -0,0 +1,15 @@
+module amodule
+
+pub fn iadd(x int, y int) int {
+	return x + y
+}
+
+pub fn imul(x int, y int) int {
+	return x * y
+}
+
+///////////////////////////////////////
+
+fn private_isub(x int, y int) int {
+  return x - y
+}
diff --git a/vlib/compiler/tests/repl/repl_test.v b/vlib/compiler/tests/repl/repl_test.v
index 21160c3159..1940fcc9a1 100644
--- a/vlib/compiler/tests/repl/repl_test.v
+++ b/vlib/compiler/tests/repl/repl_test.v
@@ -1,3 +1,5 @@
+module main
+
 import os
 import compiler.tests.repl.runner
 import benchmark