diff --git a/scripts/assets/test_file_exemptions.textproto b/scripts/assets/test_file_exemptions.textproto
index 94ebe621a53..02d22431745 100644
--- a/scripts/assets/test_file_exemptions.textproto
+++ b/scripts/assets/test_file_exemptions.textproto
@@ -4106,10 +4106,6 @@ test_file_exemption {
   exempted_file_path: "testing/src/main/java/org/oppia/android/testing/math/MathParsingErrorSubject.kt"
   test_file_not_required: true
 }
-test_file_exemption {
-  exempted_file_path: "testing/src/main/java/org/oppia/android/testing/math/TokenSubject.kt"
-  test_file_not_required: true
-}
 test_file_exemption {
   exempted_file_path: "testing/src/main/java/org/oppia/android/testing/mockito/MockitoKotlinHelper.kt"
   test_file_not_required: true
diff --git a/testing/src/main/java/org/oppia/android/testing/math/TokenSubject.kt b/testing/src/main/java/org/oppia/android/testing/math/TokenSubject.kt
index 737de61a7b9..49cce0f2030 100644
--- a/testing/src/main/java/org/oppia/android/testing/math/TokenSubject.kt
+++ b/testing/src/main/java/org/oppia/android/testing/math/TokenSubject.kt
@@ -26,8 +26,6 @@ import org.oppia.android.util.math.MathTokenizer.Companion.Token.RightParenthesi
 import org.oppia.android.util.math.MathTokenizer.Companion.Token.SquareRootSymbol
 import org.oppia.android.util.math.MathTokenizer.Companion.Token.VariableName
 
-// TODO(#4121): Add tests for this class.
-
 /**
  * Truth subject for verifying properties of [Token]s.
  *
diff --git a/testing/src/test/java/org/oppia/android/testing/math/BUILD.bazel b/testing/src/test/java/org/oppia/android/testing/math/BUILD.bazel
index 52d56ecfcfd..63cb143e73e 100644
--- a/testing/src/test/java/org/oppia/android/testing/math/BUILD.bazel
+++ b/testing/src/test/java/org/oppia/android/testing/math/BUILD.bazel
@@ -82,3 +82,17 @@ oppia_android_test(
         "//third_party:robolectric_android-all",
     ],
 )
+
+oppia_android_test(
+    name = "TokenSubjectTest",
+    srcs = ["TokenSubjectTest.kt"],
+    custom_package = "org.oppia.android.testing.math",
+    test_class = "org.oppia.android.testing.math.TokenSubjectTest",
+    test_manifest = "//testing:test_manifest",
+    deps = [
+        "//testing/src/main/java/org/oppia/android/testing/math:token_subject",
+        "//third_party:com_google_truth_truth",
+        "//third_party:junit_junit",
+        "//third_party:robolectric_android-all",
+    ],
+)
diff --git a/testing/src/test/java/org/oppia/android/testing/math/TokenSubjectTest.kt b/testing/src/test/java/org/oppia/android/testing/math/TokenSubjectTest.kt
new file mode 100644
index 00000000000..a50967aa57d
--- /dev/null
+++ b/testing/src/test/java/org/oppia/android/testing/math/TokenSubjectTest.kt
@@ -0,0 +1,217 @@
+package org.oppia.android.testing.math
+
+import org.junit.Assert.assertThrows
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.junit.runners.JUnit4
+import org.oppia.android.util.math.MathTokenizer.Companion.Token
+
+/** Tests for [TokenSubject]. */
+@RunWith(JUnit4::class)
+class TokenSubjectTest {
+
+  @Test
+  fun testTokenSubject_passesWithCorrectStartIndex() {
+    val token = Token.PositiveInteger(42, 10, 15)
+    TokenSubject.assertThat(token).hasStartIndexThat().isEqualTo(10)
+  }
+
+  @Test
+  fun testTokenSubject_failsWithIncorrectStartIndex() {
+    val token = Token.PositiveInteger(42, 10, 15)
+    assertThrows(AssertionError::class.java) {
+      TokenSubject.assertThat(token).hasStartIndexThat().isEqualTo(11)
+    }
+  }
+
+  @Test
+  fun testTokenSubject_passesWithCorrectEndIndex() {
+    val token = Token.PositiveInteger(42, 10, 15)
+    TokenSubject.assertThat(token).hasEndIndexThat().isEqualTo(15)
+  }
+
+  @Test
+  fun testTokenSubject_failsWithIncorrectEndIndex() {
+    val token = Token.PositiveInteger(42, 10, 15)
+    assertThrows(AssertionError::class.java) {
+      TokenSubject.assertThat(token).hasEndIndexThat().isEqualTo(14)
+    }
+  }
+
+  @Test
+  fun testTokenSubject_passesWithCorrectPositiveIntegerValue() {
+    val token = Token.PositiveInteger(42, 10, 15)
+    TokenSubject.assertThat(token).isPositiveIntegerWhoseValue().isEqualTo(42)
+  }
+
+  @Test
+  fun testTokenSubject_failsWithIncorrectPositiveIntegerValue() {
+    val token = Token.PositiveInteger(42, 10, 15)
+    assertThrows(AssertionError::class.java) {
+      TokenSubject.assertThat(token).isPositiveIntegerWhoseValue().isEqualTo(45)
+    }
+  }
+
+  @Test
+  fun testTokenSubject_passesWithCoreectPositiveRealNumberValue() {
+    val token = Token.PositiveRealNumber(3.14, 10, 15)
+    TokenSubject.assertThat(token).isPositiveRealNumberWhoseValue().isEqualTo(3.14)
+  }
+
+  fun testTokenSubject_failsWithIncorrectPositiveRealNumberValue() {
+    val token = Token.PositiveRealNumber(3.14, 10, 15)
+    assertThrows(AssertionError::class.java) {
+      TokenSubject.assertThat(token).isPositiveRealNumberWhoseValue().isEqualTo(25)
+    }
+  }
+
+  @Test
+  fun testTokenSubject_passesWithCorrectVariableName() {
+    val token = Token.VariableName("x", 10, 15)
+    TokenSubject.assertThat(token).isVariableWhoseName().isEqualTo("x")
+  }
+
+  @Test
+  fun testTokenSubject_isVariableWhoseName_incorrectName_fails() {
+    val token = Token.VariableName("x", 10, 15)
+    assertThrows(AssertionError::class.java) {
+      TokenSubject.assertThat(token).isVariableWhoseName().isEqualTo("y")
+    }
+  }
+
+  @Test
+  fun testTokenSubject_passesWithCorrectFunctionNameAndAllowedStatus() {
+    val token = Token.FunctionName("sqrt", true, 10, 15)
+    TokenSubject.assertThat(token)
+      .isFunctionNameThat()
+      .hasNameThat().isEqualTo("sqrt")
+  }
+
+  @Test
+  fun testTokenSubject_failsWithIncorrectFunctionNameAndAllowedStatus() {
+    val token = Token.FunctionName("sqrt", true, 10, 15)
+    assertThrows(AssertionError::class.java) {
+      TokenSubject.assertThat(token)
+        .isFunctionNameThat()
+        .hasNameThat().isEqualTo("sine")
+    }
+  }
+
+  @Test
+  fun testTokenSubject_symbolIsMinusSymbol() {
+    val token = Token.MinusSymbol(10, 11)
+    TokenSubject.assertThat(token).isMinusSymbol()
+  }
+
+  @Test
+  fun testTokenSubject_symbolIsSquareRootSymbol() {
+    val token = Token.SquareRootSymbol(10, 11)
+    TokenSubject.assertThat(token).isSquareRootSymbol()
+  }
+
+  @Test
+  fun testTokenSubject_symbolIsPlusSymbol() {
+    val token = Token.PlusSymbol(10, 11)
+    TokenSubject.assertThat(token).isPlusSymbol()
+  }
+
+  @Test
+  fun testTokenSubject_symbolIsMultiplySymbol() {
+    val token = Token.MultiplySymbol(10, 11)
+    TokenSubject.assertThat(token).isMultiplySymbol()
+  }
+
+  @Test
+  fun testTokenSubject_symbolIsDivideSymbol() {
+    val token = Token.DivideSymbol(10, 11)
+    TokenSubject.assertThat(token).isDivideSymbol()
+  }
+
+  @Test
+  fun testTokenSubject_symbolIsExponentiationSymbol() {
+    val token = Token.ExponentiationSymbol(10, 11)
+    TokenSubject.assertThat(token).isExponentiationSymbol()
+  }
+
+  @Test
+  fun testTokenSubject_symbolIsEqualsSymbol() {
+    val token = Token.EqualsSymbol(10, 11)
+    TokenSubject.assertThat(token).isEqualsSymbol()
+  }
+
+  @Test
+  fun testTokenSubject_symbolIsLeftParenthesisSymbol() {
+    val token = Token.LeftParenthesisSymbol(10, 11)
+    TokenSubject.assertThat(token).isLeftParenthesisSymbol()
+  }
+
+  @Test
+  fun testTokenSubject_symbolIsRightParenthesisSymbol() {
+    val token = Token.RightParenthesisSymbol(10, 11)
+    TokenSubject.assertThat(token).isRightParenthesisSymbol()
+  }
+
+  @Test
+  fun testTokenSubject_failsWithIncorrectSymbol() {
+    val token = Token.RightParenthesisSymbol(10, 11)
+    assertThrows(AssertionError::class.java) {
+      TokenSubject.assertThat(token).isMinusSymbol()
+    }
+  }
+
+  @Test
+  fun testTokenSubject_checkIsInvalidToken_passes() {
+    val token = Token.InvalidToken(10, 11)
+    TokenSubject.assertThat(token).isInvalidToken()
+  }
+
+  @Test
+  fun testTokenSubject_checkIsInvalidToken_fails() {
+    val token = Token.PositiveInteger(10, 11, 42)
+    assertThrows(AssertionError::class.java) {
+      TokenSubject.assertThat(token).isInvalidToken()
+    }
+  }
+
+  @Test
+  fun testTokenSubject_checkIsIncompleteFunctionName() {
+    val token = Token.IncompleteFunctionName(10, 11)
+    TokenSubject.assertThat(token).isIncompleteFunctionName()
+  }
+
+  @Test
+  fun testTokenSubject_functionNameSubject_nameCheck_passes() {
+    val token = Token.FunctionName("sqrt", true, 10, 15)
+    TokenSubject.assertThat(token)
+      .isFunctionNameThat()
+      .hasNameThat().isEqualTo("sqrt")
+  }
+
+  @Test
+  fun testTokenSubject_functionNameSubject_nameCheck_fails() {
+    val token = Token.FunctionName("sqrt", true, 10, 15)
+    assertThrows(AssertionError::class.java) {
+      TokenSubject.assertThat(token)
+        .isFunctionNameThat()
+        .hasNameThat().isEqualTo("sin")
+    }
+  }
+
+  @Test
+  fun testTokenSubject_functionNameSubject_allowedPropertyCheck_passes() {
+    val token = Token.FunctionName("sqrt", true, 10, 15)
+    TokenSubject.assertThat(token)
+      .isFunctionNameThat()
+      .hasIsAllowedPropertyThat().isTrue()
+  }
+
+  @Test
+  fun testTokenSubject_functionNameSubject_allowedPropertyCheck_fails() {
+    val token = Token.FunctionName("sqrt", false, 10, 15)
+    assertThrows(AssertionError::class.java) {
+      TokenSubject.assertThat(token)
+        .isFunctionNameThat()
+        .hasIsAllowedPropertyThat().isTrue()
+    }
+  }
+}