diff --git a/crates/oxc_minifier/tests/ast_passes/collapse_variable_declarations.rs b/crates/oxc_minifier/tests/ast_passes/collapse_variable_declarations.rs
new file mode 100644
index 0000000000000..862fdc63fb3a9
--- /dev/null
+++ b/crates/oxc_minifier/tests/ast_passes/collapse_variable_declarations.rs
@@ -0,0 +1,84 @@
+use oxc_minifier::CompressOptions;
+
+fn test(source_text: &str, expected: &str) {
+    let options = CompressOptions::default();
+    crate::test(source_text, expected, options);
+}
+
+fn test_same(source_text: &str) {
+    test(source_text, source_text);
+}
+
+#[test]
+fn test_disabled() {
+    let options = CompressOptions { join_vars: false, ..Default::default() };
+    crate::test("let a; let b;", "let a;let b;", options);
+}
+
+#[test]
+fn join_lets() {
+    test("let a;", "let a;");
+    test("let a; let b;", "let a,b;");
+    test("let a = 1; let b = 2;", "let a=1,b=2;");
+    test("let a = 1; let b;", "let a=1,b;");
+    test("let a; let b = 2;", "let a,b=2;");
+}
+
+#[test]
+fn join_vars() {
+    test("var a; var b;", "var a,b;");
+    test("var a = 1; var b = 2;", "var a=1,b=2;");
+    test("var a = 1; var b;", "var a=1,b;");
+    test("var a; var b = 2;", "var a,b=2;");
+}
+
+#[test]
+fn join_const() {
+    test("const a; const b;", "const a,b;");
+    test("const a = 1; const b = 2;", "const a=1,b=2;");
+}
+
+#[test]
+fn no_join_require() {
+    test_same("var a = require('a'); var b = require('b');");
+    test_same("const a = require('a'); const b = require('b');");
+    test_same("let a = require('a'); let b = require('b');");
+    test_same("var a = 1; var b = require('b');");
+    // Should these not merge?
+    test("var a = require('a'); var b = 1;", "var a = require('a'), b = 1;");
+    test(
+        "var a = require('a'); var b = 1; var c = require('c');",
+        "var a = require('a'), b = 1; var c = require('c');",
+    );
+}
+
+#[test]
+fn join_mixed_all_different() {
+    // different
+    test("let a = 1; var b = 2;", "let a=1;var b=2;");
+    test("let a = 1; const b = 2;", "let a=1;const b=2;");
+}
+
+#[test]
+fn join_mixed_interspersed() {
+    test("let a = 1; var b = 2; let c = 3;", "let a=1;var b=2;let c=3;");
+}
+
+#[test]
+fn join_mixed_same_adjacent() {
+    test("let a = 1; var b = 2; var c = 3;", "let a=1;var b=2,c=3;");
+    test("let a = 1; let b = 2; var c = 3;", "let a=1,b=2; var c=3;");
+}
+
+#[test]
+fn interspersed_statements() {
+    test_same("var x = 1; assert.equals(x, 1); var x = 2;");
+    test("var x = 1; if (y) { x = 2 } var x = 2;", "var x = 1; if (y) x = 2; var x = 2;");
+}
+
+#[test]
+fn interspersed_expressions() {
+    test_same("var a = 1; a = 2; var b = 3;");
+    test_same("var a = 1; a = 2; var a = 3;");
+    test_same("var a = 1; a += 1; var b = 3;");
+}
diff --git a/crates/oxc_minifier/tests/ast_passes/mod.rs b/crates/oxc_minifier/tests/ast_passes/mod.rs
index 88d302d7e20b6..efaad4159ecff 100644
--- a/crates/oxc_minifier/tests/ast_passes/mod.rs
+++ b/crates/oxc_minifier/tests/ast_passes/mod.rs
@@ -1,3 +1,4 @@
+mod collapse_variable_declarations;
 mod dead_code_elimination;
 
 use oxc_minifier::CompressOptions;